Versions:
Issue persists in dev snapshot: https://builds.jabref.org/master/JabRef-4.3-dev--snapshot--2018-04-26--master--7629b3171.jar

Tested on Windows 7 with Java x64 Build 1.8.0_162-b12

Issue:

On a database with about 2000 entries, most of them with associated PDFs, the search box behaves even worse in 4.2 than it did in 4.1.

Problems are:

1. Random duplication of entered search strings (see issue Search box erroneously duplicates entered query strings #3921 )
2. Random lockups of the complete search box (no new text can be entered, old text cannot be deleted, no text can be marked)
3. Random vertical shifts of the already entered characters as if a new blank line was added.

Problems 1) and 2) were already present in 4.1, Problem 3) seems to be a new addition of 4.2. I also have the feeling that the crashes will come faster now, on average it takes only 3-4 searches until something bad happens and you have to restart JabRef entirely.