Merge on import

I am often importing articles via the firefox plugin. If a match already exists, as is often the case with trying to add the published paper information to a preprint, a merge warning appears, and the import window offers up the window to select for duplication, with the options of Remove Old Entry, Keep Both or Keep merged entry only.
However when selecting “Keep merged entry only” I cannot actually complete the import.
How can I directly merge the entries on import?

Hello whitecold, which version of JabRef is this?

I am currently using JabRef 5.7

JabRef 5.7–2022-08-05–73c111c / Linux 5.15.0-58-generic amd64

would you mind trying JabRef 5.9 or the development version? There have been some great changes to the entry merge editor, which were first released in JabRef 5.8.

I did upgrade to 5.9.
Unfortunately the behavior presists when selecting merge entries, it is still impossible to complete the import.
Playing around with it, I found that Preprints (listed as TechReports) are now no longer recognized as duplicates during the Import window prompt, while they were recognized under 5.7.

Can you provide the two entries as an example? Just copy the data from the {} biblatex source tab. Will try to reproduce.

Unfortunately I am not able to reproduce the issue with the duplicates not being recognized, as the original entry got overwritten, and others seem to be working now.