Ah, you are correct. My new code thinks those mounted volumes are mounted DMG files. DMG files look bad if they have custom background and TotalFinder adopts them.
A temporary solution would be this Terminal tweak:
defaults write com.binaryage.totalfinder TotalFinderDoNotIgnoreDMG -bool true
You have to restart Finder.app via CMD+OPT+ESC and then launch
/Applications/TotalFinder.app again for this to take effect.
I will try to solve it and get back to you.