Manually copying and pasting a diff id into the subpage argument for Special:Thanks (e.g. if I edited my user page with a revid of 987654321, navigating to Special:Thanks/987654321) and clicking the button gives me this informative error message:

Thank action failed (error code: $1). Please try again.

There are a number of things wrong here:

• If it's possible to disable the confirmation button client-side, we should be doing that (with an appropriate error message)
• "$1" is a pretty bad error code, and probably indicates a string substitution issue
• "Thank action failed" is a pretty bad error message, and probably indicates that someone didn't think of this particular edge case
• "Please try again" probably isn't the best thing to be advising users. For that matter, is it even a good idea to be asking users to try again in every case, given that the relatively lightweight nature of the thanking system means that an error that makes the thank action fail might *not* be solvable by trying again? (On this point, I'm probably wrong, but clarification would be welcome.)

Admittedly, it's an edge case, but fixing that "$1" might be useful in error display in general for the Thanks system, not just this case.