I use the "Dark Theme By Hille - Mod By Juress", and every time I close my browser, my theme resets to the default white theme, and I have to re-select the dark theme every time. I cant say this is a huge deal breaker, but it is certainly annoying since themes are the main reason I use BBL (I find the white theme to be straining to stare at for too long).
Strange, this is the first time i've heard about it.
I suppose you allready tried to reinstall the plugin. I guess this must be some problem with bblog not being able to store settings on your computer.