In Preferences, Display, Colors and Fonts, there appears to be a checkbox or some other control partially hidden behind the listbox on the right-hand side of the preferences dialog.
I am using on Windows 10. Directory Opus version 12.8 x64 (build 6688).
Strange...
Which item is selected when you see that? Can we see a screenshot of the whole window?
Well, naturally I am now unable to reproduce what I was seeing. If it happens again I'll try to take more screenshots and figure out steps to reproduce.