My wife's office ran into EXACT SAME issue. They too use CMS1500 forms in place of Super Bills/Charge Slips to give to their billing company. I wrote them many emails. In fact, they acknowledge that it is indeed a bug introduced in Version 6.6.1. AC does not seem to care enough to fix this right away.

Well I have solution. I sent you (tfh6044) a detailed email to your gmail account explaining how problem was fixed.