I am experiencing this same set of problems, as the Jira plugin does not post to
projects which are named entirely with numbers. I can confirm that it will post
to an all letter project, or to a project which has letters and numbers.
However it does not post to a project which is fully a number (our standard format)
For instance the plugin is not able to determine the project number for the
following commit log:
4313-48 - Updated the default part number generated.
yet it has no problem with a project made up with words.
It looks like a Regex made up simply of "[A-Za-z0-9]+" would allow the Jira
plugin to post to projects named only numbers.