I found another poor pt soul that had this issue with PT, someone suggested it might be a plug in 'hogging the TAB function'. I'm using Ozone 5 & Waves level meter.... looks like it's still here with pt 10point 00OH! :-O
My work around is to hit return (go to top of session) then return to newly made marker....boy that's a lot of keystrokes for the 'world's fastest DAW' :-O
(TAB to transient or clip boundry)
http://duc.avid.com/images/smilies/eek.gif