This fixes a bug that causes the find/replace window, after being closed, is sometimes still visible, even though the user can't interacted with it.
See bug ID: 2779346 (Transparent Find window remains visible after closing)
I tested the fix with the source code from version 5.3.1. The patch is a diff from the SVN Repository, Revision 464. This SVN version had errors compiling on my system due to some missing declarations, so I wasn't able to test it with the newest version, but I believe it will still work and fix the bug.