SPRM 4 problem

Phew... FINALLY got it working properly in DVD player.
Each track jumped to my "return?" script which checked SPRM4 to get the number of the last track played, which worked in the simulator, but not in "real life". So I set a GPRM track counter instead and that works.
Isn't SPRM 4 meant to be thhe last track played number, or am I making a mistake? The track jumps straight to the script, so I'd have thought using SPRM 4 should have worked...
Well, my "time saving" template has used up a couple of days, but should come into its own next time someone wants a play-all: no more messing around in FC pro making showreels, and making all those Stories in DVD Studio.
- Paddy