Material Panner displays unusual behavior with timeline update

A material with a panner displays unusual behavior when the value of the panner's speed it dependant on a timeline. As time spent in the project increases the speed of the material while changing value appears to increase. This behavior does not seem intended.

Regression:
This behavior occurs in 4.14.3, 4.15.3, and 4.16 binary builds of the engine

1. Open TestProject Provided
2. PIE and move into and out of the trigger volume several times
   Result: The material speeds up rapidly when changing values from the timeline, the speed increases over time
   Expected result: The material displays a consistent speed when changing values via the timeline.