Morph Target Sets to Zero When Transitioning From 1 to -1 Causing Flickering

-Morph target cycles through all values instead of only alternating between 1 and -1
-Couldn't reproduce in 4.17
-attached a test morph target asset

Link to example video from user:
[Link Removed]

1. Download attached project
2. PlE
3. See the box shape in the flickering

Expected: Morph target changes between -1 and 1 without resetting to 0
Results: Morph alternates between -1 and 1 but resets to 0