> C:\dev\ruby\downloads>gem search rdoc
> C:/installs/ruby_trunk_installed/lib/ruby/gems/1.9.1/specifications/rdoc-data-2.5.1.gemspec:18:
> [BUG] gc_sweep(): unknown data type 0x0(0x230bd19)
> ruby 1.9.3dev (2010-07-08) [i386-mingw32]

I seem unable to reproduce this now in trunk:

ruby 1.9.3dev (2010-08-26 trunk 29104) [i386-mingw32]

so I'll assume it's fixed for now.
Thanks!
-rp