Question on pot limit betting rules

[memphis57]

I was playing in a PL tourney on Stars last night, and there was about 2000 in the pot. It was heads up, opponent bet 1300, and on my turn only 3 buttons showed and no slide bar. Buttons were for fold, bet 1300 (call) and bet 3300 (raise by preaction pot amount). Why wasn't I allowed to raise some other amount less than the full 2000?

Also, just a good simple description of betting rules would be appreciated. Presumably there's one on PS somewhere but I can't find it.