JabRef 5.1--2020-04-12--771af5d
Linux 5.4.19-050419-generic amd64
Java 14

• I have tested the latest development version from http://builds.jabref.org/master/ and the problem persists

Steps to reproduce the behavior:

1. Open two different bibfiles (A and B) with a couple of entries
2. Select and copy one or more entries from the entry table of file A (via Ctr-C or via the Copy button).
3. Switch to the entry table of file B.
4. Use the Paste button.
5. (For me) The entry is not inserted in file B.
6. Use Ctr-V instead and the entry is inserted in file B.