+1 I have the same issue.

I have a GET request that contains url encoded data like: Stuff%20-%20Other 
(translated to "Stuff - Other"). In rails3.1 this crashes with  invalid 
%-encoding   rack (1.3.2) lib/rack/backports/uri/common.rb:67:in 
`decode_www_form_component'

It's quite a nasty bug.