There is a hard limit on the number of pairs and proxies. This is from the C++ library, and not something pybox2d introduced.
If you want > 1024 proxies, you will have to modify b2_maxProxies in Box2D\Common\b2Settings.h and recompile (instructions here
Ah thanks, that explains that part anyway.
I haven't heard about adding 128 bodies per step, but perhaps your bodies had 8 shapes each (128*8=1024)? If you do modify the settings, be sure to use a power of two, by the way.
No, the bodies have 1 shape each, and if I add the same bodies but spread out over alot of steps it works perfectly, until i reach the 1024 limit that is