@matheos: please can you change the thread title to something more descriptive and helpful like "mintInstall 6.3.5 - offline hangs on screenshot dl" or something similar.
I can confirm this bug *for browsing apps not browsed before*, apps for which I already have the screenshot aren't a problem. Looking at the code (frontend.py), this is really strange as the download screenshot stuff should all be occuring in a separate thread, and hence not affect the main app. However, it can't be threading properly because the app's reviews list isn't populated while retrieving the screenshot is hanging.
Ok, I first thought the reason for this is the data locks that threading has to use in order to prevent accessing the same stuff at the same time as another thread (or, if it doesn't do this automatically, then the simultaneous access of wTree/model from the main thread). However, this can't be the case, because it works in the online mode, or perhaps it just happens fast enough that it's complete by the time the data is needed again. It could also be to do with using os.system, rather than urllib: http://code.activestate.com/recipes/496685/
Basically, I can't identify the exact source of the problem, but this definitely needs looking at in more detail.
If you have a question that has been answered and solved, then please edit your original post and put a [SOLVED] at the end of your subject header
Hint - use a google search including the search term site:forums.linuxmint.com