Colon in User Defined Fields hyperlinking: turn off?

We’ve noticed that if there’s a colon in any of the user defined fields, RefMan hyperlinks the field. Sometimes we love this (it will hyperlink a PubMed ID entered as PM:1234 to the PubMed record), but other times not. Is there a way to turn this off for some of the user defined fields? 

I’m using RefMan 11 (is this changed in RM12?)

Many thanks, and happy long weekend!