Ruby crashing: pointer being freed was not allocated

I starting seeing this error quite frequently the past couple of days:

$ rake routes ruby(38294,0x7fff70ee6ca0) malloc: *** error for object 0x100000000: pointer being freed was not allocated *** set a breakpoint in malloc_error_break to debug Abort trap

Rails server crashes, some rake tasks crash, but not consistently.

I have: - removed ruby 1.9.2-p180 and reinstalled (via rvm) - delete gemset and re-installed all gems

Any ideas why?