"Rename Records" - regexp trouble

Hi! I’m trying to bulk-rename records via Automator but I’m constantly running into problems with the regexp. An example: The search string

^TP- (.*)$

seems to work fine but the replace string

TP: \1

produces the error “Syntax error in expression “TP: \1”:invalid backref number/name (-1704)”. The reason probably is a very obvious one but I can’t seem to figure it out right now. I’m using DTP 1.3beta3. Any hint is appreciated! Thanks!