I use 1.6.1 and it seems to really choke on 7z files, RAM usage goes through the roof. It seems that it actually only does the real choking if I try to cancel, it takes a few minutes or so to actually do the canceling. I tried 7zX and it works fine. Considered using the p7zip file instead of just libxad?
Of course, it could be because 7zip doesn't provide a progress bar and it was working fine, I just didn't see any progress.