And say "That's not what you asked for. What you're asking for is additional development and subject to normal scheduling concerns." :-) Of course, when they start imploding, you can gently remind them that they are free to prioritise any development they want in before any amount of bugs they have submitted.
Back at the place we were using RT, we did that once or twice. Taught them to check what they asked for before saying 'it doesn't work right'.
Wade.