I've wondered the same thing. I always keep some of my regular mags loaded - for several months sometimes. I've never had any problem.
I hear people always preaching not to do it, but I haven't seen any problems.
I would suppose that the spring material in the Russian/Romanian Drums are similiar. I've been wanting to p/u a couple and keep one loaded just to experiment. I'm kinda cheap though. I've been looking to get them for 70ish shipped and keep missing them on the EE.
You'd think with them being military type equipment, that they would be built to stay loaded for an extended time. I can't see troops being coached to:
"Leave 'em unloaded men - then when you see the enemy coming - then and only then - load the drums up and let 'em have it. But remember, after the shootings over - get them things unloaded."