The last time they polled they did it under a different system and they did it in May.
For full disclosure (and for those who can't read the poll section for PA):
Rasmussen:
D - 56 R - 33 D+23 May 22
D - 52 R - 37 D+15 Jun 19
D - 50 R - 39 D+11 July 26
D - 48 R - 40 D+8 Aug 21
Q Uni Poll:
D - 49 R - 36 D+13 May 8
D - 52 R - 34 D+18 Jun 19
D - 48 R - 42 D+6 Aug 13
SV:
D - 49 R - 41 D+8 May 7
D - 49 R - 40 D+9 Jun 11
D - 50 R - 40 D+10 July 16
D - 47 R - 41 D+6 Aug 13
Those three are the only ones which have monthly polled PA since May. Muhlenberg and Franklin and Marshall have run August polls, but none before that this summer.
Here's the poll section for PA.