I am trying to use the "List with Comment" question and am finding that the longest question code I can use via the web interface is only 5 characters long. Is this a bug or a 'feature'? Is there a work around?

Are you talking about the question code or the answer code?

Question code.

Hmmm, what version are you using? I just created a list with comment type question with the following question code (this was the maximum): a1234567891234567891

So this are 20 digits.

Sure you are not referring to this:
www.limesurvey.org/en/community-services...en-the-question-code