Regular Expressions, change from 2.47? to 2.49

there appears to have been a change in using character classes with anchors within negative lookbehind assertions.

example, around 2.47 this worked (?<!^|\s|\d) Now with 2.49 this does not.

Separately, (?<!^) , (?<!\s\d) , both work. Is this a bug? Or, is there a solution to my query?

This is the full regexp that did work and now does not. (?<!^|\s|\d)(.)([^\W\d_])(?!.|\s|$)

Thank-you in advance!

Alternations in a lookbehind expression need to be of equal length in Mp3tag, so this expression never really worked.
The only change is that now it raises an error message.
See discussion here.