Desktop WPF application slowed by DWM operations

Question

We have a WPF application, that sporadically (rarely) becomes very sluggish. We've managed to capture a WPA trace (aka xperf), and it distinctly shows lags in application activity - and at the same time a distinct rise in dwm.exe activity.

I couldn't extract from the stacks any useful insights into what is going on. The application seems to spend a lot of time in the following stack:

And dwm seems to spend a lot of time in the following stack:

Can anyone shed some light on what's slowing the app down?

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Edit: here's the WPA pkg (350k), in case you'd be willing to take a look.