I have this exact issue when applying any theme from theme manager. That link just above doesn't really solve the problem (I think) because this is true with every theme I've tried to apply. Even ones with (supposedly) correct links and supporting Win7.
So, you applied beta version:
"I simply upgraded to v3.98 BETA and it started working correctly"...
Beta version of what? MyColors? or Theme Manager? And where did you get it? Impulse shows me only the versions that I have installed with no option to get it. I've searched around the site (for a couple of hours at least) but can't find anything.
So, show me the way brother..