Illformed requirement on edge with certain versions of ruby

hi everyone, I'm using latest edge snapshot.

upon script/server:

/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems/requirement.rb:144:in `parse': Illformed requirement ["~> 1.1.pre"] (ArgumentError)
	from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems/requirement.rb:70:in `initialize'
	from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems/requirement.rb:69:in `map'
	from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems/requirement.rb:69:in `initialize'
	from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems/requirement.rb:42:in `new'
	from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems/requirement.rb:42:in `create'
	from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems/dependency.rb:29:in `initialize'
	from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems.rb:307:in `new'
	from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems.rb:307:in `activate'
	 ... 8 levels...
	from /Users/kain/Sites/careme/vendor/rails/railties/lib/commands/server.rb:1
	from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems/custom_require.rb:27:in `gem_original_require'
	from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems/custom_require.rb:27:in `require'
	from script/server:3

this is with leopard vanilla ruby. I tried also with a not so recent version (20090113) of Ruby Enterprise Edition and got the same error; I updated REE (20090421) and the problem disappeared.