After starting mp3tag the tag panel has a wrong width and i can not see the drop-down buttons. They appear only after changing the width with the slider
I can't reproduce it and also after a thorough code review, I can't see what's causing the issue.
Which version of Windows are you using and what are your DPI settings?
It's Windows 10 Version 1809, using three screens - two wih 2560x1440, one with 1680x1050px. I 've just tested it. It happens on the big screens only. When started on a 2560x1440px screen this problem occurs. no problem at 1680x1050.
I've tried with my 2880x1800 (also at 2560x1600) with no success at reproducing the issue.
I'll have to keep that open for now.
Maybe as a follow-up question: are you running any third-party software that might interfere with the resolution, DPI or reported window sizes?