Ask HN: Trawl for DSL debugging anecdotes

I'm looking for some (serious) anecdotes describing debugging experiences of domain-specific language programs. In particular, I want to know about particularly thorny bugs which caused you lots of headaches. I'd like to know how you cracked the problem-- what techniques/tools you used: did you 'home in' on the bug systematically, did you use a special-purpose debugger, etc. A very brief stream-of-consciousness reply (right now!) would be better than a carefully-worked-out story. If you want to keep it private, my email is in my profile.

(Motivation: For my Master's research I will study DSL debugging. DSLs get lots of hype---from Paul Graham, Dave Thomas, Charles Simonyi, Sergey Dmitriev, the Ruby crowd and others---but debugging issues are rarely discussed. This trawl is inspired by Marc Eisenstadt's "Tales of Debugging from the Front Lines." In fact I ripped the text above from his paper.)

Thanks!