Disturbing Java Error in jabref

Hi,
working with jabref 5. on linux mint: What means following error message?
Roody

java.lang.IllegalStateException: Task must only be used from the FX Application Thread
at org.jabref.merged.module/javafx.concurrent.Task.checkThread(Unknown Source)
at org.jabref.merged.module/javafx.concurrent.Task.isRunning(Unknown Source)
at org.jabref.merged.module/org.controlsfx.control.textfield.AutoCompletionBinding.onUserInputChanged(Unknown Source)
at org.jabref.merged.module/org.controlsfx.control.textfield.AutoCompletionBinding.setUserInput(Unknown Source)
at org.jabref/org.jabref.gui.autocompleter.AutoCompletionTextInputBinding.setUserInputText(Unknown Source)
at org.jabref/org.jabref.gui.autocompleter.AutoCompletionTextInputBinding.lambda$new$0(Unknown Source)
at org.jabref.merged.module/com.sun.javafx.binding.ExpressionHelper$Generic.fireValueChangedEvent(Unknown Source)
at org.jabref.merged.module/com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(Unknown Source)
at org.jabref.merged.module/javafx.scene.control.TextInputControl$TextProperty.fireValueChangedEvent(Unknown Source)
at org.jabref.merged.module/javafx.scene.control.TextInputControl$TextProperty.markInvalid(Unknown Source)
at org.jabref.merged.module/javafx.scene.control.TextInputControl$TextProperty.controlContentHasChanged(Unknown Source)
at org.jabref.merged.module/javafx.scene.control.TextInputControl.lambda$new$0(Unknown Source)
at org.jabref.merged.module/com.sun.javafx.binding.ExpressionHelper$SingleInvalidation.fireValueChangedEvent(Unknown Source)
at org.jabref.merged.module/com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(Unknown Source)
at org.jabref.merged.module/javafx.scene.control.TextArea$TextAreaContent.insert(Unknown Source)
at org.jabref.merged.module/javafx.scene.control.TextInputControl.replaceText(Unknown Source)
at org.jabref.merged.module/javafx.scene.control.TextInputControl.filterAndSet(Unknown Source)
at org.jabref.merged.module/javafx.scene.control.TextInputControl$TextProperty.doSet(Unknown Source)
at org.jabref.merged.module/javafx.scene.control.TextInputControl$TextProperty.set(Unknown Source)
at org.jabref.merged.module/javafx.scene.control.TextInputControl$TextProperty.set(Unknown Source)
at org.jabref.merged.module/javafx.beans.property.StringProperty.setValue(Unknown Source)
at org.jabref.merged.module/javafx.beans.property.StringProperty.setValue(Unknown Source)
at org.jabref.merged.module/com.sun.javafx.binding.BidirectionalBinding$TypedGenericBidirectionalBinding.changed(Unknown Source)
at org.jabref.merged.module/com.sun.javafx.binding.ExpressionHelper$Generic.fireValueChangedEvent(Unknown Source)
at org.jabref.merged.module/com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(Unknown Source)
at org.jabref.merged.module/javafx.beans.property.StringPropertyBase.fireValueChangedEvent(Unknown Source)
at org.jabref.merged.module/javafx.beans.property.StringPropertyBase.markInvalid(Unknown Source)
at org.jabref.merged.module/javafx.beans.property.StringPropertyBase.set(Unknown Source)
at org.jabref.merged.module/javafx.beans.property.StringPropertyBase.set(Unknown Source)
at org.jabref.merged.module/javafx.beans.property.StringProperty.setValue(Unknown Source)
at org.jabref.merged.module/javafx.beans.property.StringProperty.setValue(Unknown Source)
at org.jabref/org.jabref.gui.util.BindingsHelper$BidirectionalBinding.updateLocked(Unknown Source)
at org.jabref/org.jabref.gui.util.BindingsHelper$BidirectionalBinding.changedB(Unknown Source)
at org.jabref.merged.module/com.sun.javafx.binding.ExpressionHelper$SingleChange.fireValueChangedEvent(Unknown Source)
at org.jabref.merged.module/com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(Unknown Source)
at org.jabref.merged.module/javafx.beans.binding.ObjectBinding.invalidate(Unknown Source)
at org.jabref.merged.module/com.sun.javafx.binding.BindingHelperObserver.invalidated(Unknown Source)
at org.jabref.merged.module/com.sun.javafx.collections.MapListenerHelper$Generic.fireValueChangedEvent(Unknown Source)
at org.jabref.merged.module/com.sun.javafx.collections.MapListenerHelper.fireValueChangedEvent(Unknown Source)
at org.jabref.merged.module/com.sun.javafx.collections.ObservableMapWrapper.callObservers(Unknown Source)
at org.jabref.merged.module/com.sun.javafx.collections.ObservableMapWrapper.put(Unknown Source)
at org.jabref/org.jabref.model.entry.BibEntry.setField(Unknown Source)
at org.jabref/org.jabref.model.cleanup.FieldFormatterCleanup.cleanupSingleField(Unknown Source)
at org.jabref/org.jabref.model.cleanup.FieldFormatterCleanup.cleanupAllFields(Unknown Source)
at org.jabref/org.jabref.model.cleanup.FieldFormatterCleanup.cleanup(Unknown Source)
at org.jabref/org.jabref.logic.exporter.BibDatabaseWriter.applySaveActions(Unknown Source)
at org.jabref/org.jabref.logic.exporter.BibDatabaseWriter.savePartOfDatabase(Unknown Source)
at org.jabref/org.jabref.logic.exporter.BibDatabaseWriter.saveDatabase(Unknown Source)
at org.jabref/org.jabref.gui.exporter.SaveDatabaseAction.saveDatabase(Unknown Source)
at org.jabref/org.jabref.gui.exporter.SaveDatabaseAction.doSave(Unknown Source)
at org.jabref/org.jabref.gui.exporter.SaveDatabaseAction.save(Unknown Source)
at org.jabref/org.jabref.gui.dialogs.AutosaveUIManager.listen(Unknown Source)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.base/java.lang.reflect.Method.invoke(Unknown Source)
at org.jabref.merged.module/com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Unknown Source)
at org.jabref.merged.module/com.google.common.eventbus.Subscriber$SynchronizedSubscriber.invokeSubscriberMethod(Unknown Source)
at org.jabref.merged.module/com.google.common.eventbus.Subscriber$1.run(Unknown Source)
at org.jabref.merged.module/com.google.common.util.concurrent.DirectExecutor.execute(Unknown Source)
at org.jabref.merged.module/com.google.common.eventbus.Subscriber.dispatchEvent(Unknown Source)
at org.jabref.merged.module/com.google.common.eventbus.Dispatcher$PerThreadQueuedDispatcher.dispatch(Unknown Source)
at org.jabref.merged.module/com.google.common.eventbus.EventBus.post(Unknown Source)
at org.jabref/org.jabref.logic.autosaveandbackup.AutosaveManager.lambda$listen$0(Unknown Source)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
at java.base/java.util.concurrent.FutureTask.run(Unknown Source)
at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(Unknown Source)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.base/java.lang.Thread.run(Unknown Source)

Hi,

please try the latest development version 5.1 from here. The issue is fixed there. The new version will soon be released.
https://builds.jabref.org/master/
Remember to make a backup of your library before trying out the new version.