Perplexing usescrdim/usedstdim behavior

I'm new to jitter and trying to implement a zooming in function on an image viewer app of sorts. To start i copied part of Tutorial 14 and put it in a subpatch just before my jit.pwindow:

The problem begins when you click either toggle sending a usesrcdim or usedstdim message. After that when you turn the page in my img viewer it actually turns 2 pages. So my question is does sending a jit.matrix one of these messages make TWO of something happen where otherwise it would happen only once? I can't find the source of this doubling for the life of me. The strange thing is there's absolutely nothing after that jit.matrix except a couple of outlets and the final pwindow and once you send one of those messages, sending the message to turn it off doesn't help. Even more confusing, it works normally if that pwindow is simply not selected, or if i set it to Ignore Clicks. Unfortunately i'm going to need that clicking functionality soon, so that's not really a solution.

I realize this is kind of a shot in the dark, but i'm completely beat. Any suggestions would be highly appreciated. I'll gladly post more of the patch, but obviously i don't expect anyone to do my diagnostic work for me. As always, i'll continue to do more reading, although i feel a little directionless at this point..