Thank you for your feedback. There was a big rewrite of the LibreOffice/OpenOffice related code in JabRef 5.7. The person responsible for the code unfortunately is not actively involved in JabRef’s development anymore and other core developers currently have set themselves different priorities (Please don’t shoot the messenger. My personal coding capabilities are very very low). JabRef developers often (but not always) follow the strategy of having rewrites of larger parts of the code at once. Switching from one context to the other takes time. I assume, fixing this issue probably requires a good understanding of LibreOffice/OpenOffice related code, otherwise somebody might have fixed it already.
Thanks for the answer. I started to wonder whether I was the only one to have this problem, which btw seems to me a major issue that may prevent the use of Jabref.
In the meanwhile I guess I’ll have to downgrade to 5.6, if possible.