ERB comments in Ruby 1.8.7
After upgrading a server to Ubuntu Intrepid I found that the Rails site's layouts broke. The problem is this issue resulting from a ERB code change in Ruby 1.8.7: if you put a # Ruby comment in a one-line <% %> block, all the content up to the next %> that's on a subsequent line is ignored.
This is really annoying, but since not everyone agrees this should work anyway you may need to work around it yourself – put the closing %> on the next line.
It's worth noting that Ruby 1.8.7 is still not recommended for Rails apps due to such issues; stick with Ruby 1.8.6 if you can. Ubuntu users can either stick with Hardy, or pin the Ruby packages to Hardy's version.