Report your bugs here - if someone else has already mentioned the same bug, just add on to their post with as much info as possible to make the hunting easier.
In Bookpedia (5.4.2), select multiple entries and choose edit (the Edit Multiple Entries window opens). Click on any textfield (with existing text) to edit the text and use the cursors keys to move the caret around. At this point the blue focus box creates a mess as it improperly draws itself within the white text area. Doesn't affect the data being entered.
Thank you so much for the detailed bug report with the steps by steps to reproduce.
Is this on Mac OS X 10.11.5 (or do we also call older OS X now macOS)? Are you on a Retina Mac? Just looking for difference that might affect the UITextfield area display.