I just declined a flag and wrote a long reason why. I wanted to check that for typos so I went to the show flags screen for the question. The message isn't displayed but there is a title set for the declined state that shows the error. Here's what I see:
' which is legitimate enough in some places but it just doesn't seem to work here. Furthermore there's no need for it here. This place is safe. It's wrapped in real quotes.
I'd just drop some of the escaping, or manually re-replace
Or display the reason on the page like you do in the timeline... Or drop the "show-flags" screen completely. Does it add anything over the timeline screen?