Camera Shake can apply a new post process material every tick when post process material has "Is Blendable" disabled

In the repro project the player camera has a post process material that slightly darkens the frame by subtracting 0.01 from the final color. When a camera animation based on a camera sequence is played, each tick a new instance of the post process material is added to the post process graph, which compounds the effects eventually leading to a black screen.

This appears to be the result of the cached blendables being appended to the existing blendables in 
UCameraAnimationSequenceCameraStandIn::ResetDefaultValues

1. Download, extract and run project from linked UDN
2. PIE and press space bar to jump

RESULT

The screen slowly fades to black.