regexp issue

Hello.

SO. I'm using regexp to convert lists of pitch values (between 1 and 88) to chord symbols, placing a "." between each and parsing them out before being sent as midi, which has been going fine so far. BUT. When regexp is given a list of two pitch values, it adds four digits to the end of the second integer.

Any ideas what's going on? And is there a way to get regexp to not do this? And if not, any thoughts on how to filter these out after the fact (bearing in mind that there will be lots of other, unproblematic chord symbols coming through regexp that won't need filtering)?

Thanks