I just downloaded the 4.1 upgrade from TMo for my bb7100t, installed it, and now it's having issues....
The display has black and white icons that are VERY basic, the text get jumbled like its just putting text on top of text, scrolling in a mune you like options turns the screen black except for the option you're, won't load themes (set to none now), and other general issues....
I had the same problem. It is because I had an "O2" theme installed prior to the upgrade. Delete the theme using the Desktop Manager and it will solve the problem. Now I will search for an updated theme like O2 for 4.1 because the default T-Mobile BB theme sucks.