The best tool for fixing bugs is the smallest possible reproducing example case.
This repo will hold a few separate, tiny and single-file yesod applications that can be used to generate tiny example cases in specific areas of yesod (hamlet, forms, persistent, etc).
Rather than creating a full-blown scaffold in which to try and reproduce, one of the files here can be taken, adjusted, and gisted as an example case for the bug you want fixed.
runhaskell minimal.hs
I will do my best to keep these compiling on the latest development snapshot of yesod -- but I certainly appreciate any help here in the form of pull requests.