HTML character escape codes from beyond

A curiousity appeared in some code I put together almost six months ago now. The site owner emailed me the output of our script which pulls together a collection of $HTTP_POST_VARS, and emails them off as a plain text document with some other information. Strewn about in one of these emails was &#somenumber; style html escaped character. The number 61623 over and over at seemingly random locations. Aside from mail(), trim() and some sundry case manipulation functions I've used nothing I can think of that would cause characters to be altered this way. Has anyone got a suggestion that might lead me in the right direction? Much thanks, Rob Salmond.