There must be a space after the issue number (ie "#12 " not "#12".) This is due to the way the RegEx is structured and will be resolved in a future release.
The RegEx needs to be updated so that it works even if there is no space after the issue number.
"This resolves #12 . thanks!" - this works
"This resolves #12 " - this works
"This resolves #12" - does not work.