iPad: Determine when the dock appears

I'm working on an app where the user can drag an image around on the screen. However, if the user holds another finger on the screen in a certain area/box, then while that finger is held, the image becomes stationary and dragging a finger around the screen manipulates the image instead of moving it.

The issue I'm running into is that when the user drags up a little from the bottom of the screen to reveal the dock (not closing the app), touchesEnded isn't called for any of the current touches, and none of the AppDelegate functions are called, so the app is still in the foreground. Googling hasn't turned up anything in regards to being able to detect when the dock is pulled up. Is there really no way to know?

This is an issue for me since otherwise I have no way of knowing that the user "lifted" their finger off of the "hold to edit" box. I can't possibly be the only one that has run into this issue.