This happens because of the DPI scale. That's why when you increase the DPI scale in Windows (different than 100%), those visual bugs are inevitable in applications not made to work with DPI scale. I think MAMEUI is not DPI scale compatible.
My frontend, Emu Loader, is not DPI scale aware either. Visual bugs like that will occur and there's nothing you can do about it.
The application needs to be fully rewritten to properly support DPI scale... and I know for a fact, it's a nightmare job.
I also have a 27" Samsung 4K monitor. My Windows DPI scale is always at 100%. When I want to work on my frontend, I always lower the resolution to 2560x1440, otherwise I can't see anything.
Ciro Alfredo Consentino
EmuCon Home: http://emuloader.mameworld.info/emucon
MCM Plus: http://mcm.mameworld.info
Edited by CiroConsentino (02/27/16 03:33 AM)