JabRef 5.15 opens bib files with Shift_JIS encoding instead of UTF-8

Recently I installed the latest official version (5.15) and opened a .bib file. For my surprise, many characters were unreadable. Then I discovered that JabRef is ?detecting? wrongly the encoding as “Shift_JIS” instead of “UTF-8”, despite the file is really saved in UTF-8 encoding by other text editors, like Sublime Text.

I decided to test many previous portable versions and discovered the problem started at version 5.7.

Next is a screen capture of the still working version 5.6, where the UTF-8 encoding is correctly assigned.

Okay that is interesting, is it plain UTF8 or UTF8 with bom?

This might refer to BOM now missing at beginning of bibliography file -- causes JabRef to not recognize existing library · Issue #9496 · JabRef/jabref · GitHub
cc @koppor

@mkaster Can we have a copy of that file? web@jabref.org

It is plain UTF-8 (as shown by hexed.it):

I can reproduce it with your file.

First JabRef tries to look for the encoding header and if not present it tries to guess the char set.
Unfortunately, the shift_jis was the first one guessed, utf 8 the second, but both with the same confidence.