I use Windows 10 x64 + NPP v8.1.4
I'm attaching an image showing the problem I'm experiencing.
Apparently, from the screenshots I've seen from others, it's not a common issue. However, I can reproduce it easily:

• Install NPP
• Defaults to light mode > no problem
• Change to dark mode > problem
• Change to light mode > no problem

Might be related to the font NPP uses for its UI? Could I change it to test if that's the case?