02Pilot
Malcontent
Just a heads-up for anyone dealing with this problem; it seems fairly common from what I've seen online. After mine ripped its second roll, I decided to take it apart and see what was going on. Long story short, after taking it apart and fiddling with a lot of things that seemed like they might be at fault but weren't, it turned out to be simply a lack of lubrication in the take-up spindle bushings causing them to bind when the film was rewound. I flushed them out with lighter fluid, then carefully dripped in a little light oil; no disassembly required (little did I know).
Rob-F
Likes Leicas
Good job, and good to know for future reference.
02Pilot
Malcontent
Full write-up with pictures here: http://filmosaur.wordpress.com/2013/02/23/workshop-rollei-35-film-ripping-on-rewind/