FBX Blendshapes - Strange Behavior on Export

For some reason, when I export a model with blendshapes as an FBX, the value of the key is being set every Update() to the value it's exported at.

For example, a blendshape exported with it's key at 0 is being told every update frame to be set to 0, and the only way to adjust at runtime seems to be telling the key a different value during LateUpdate. This behavior does not occur in .blend files.

This only occurs when the FBX model is animating, and it appears that it does not occur when the option pictured below is not checked on export (however, unchecking this causes all of the animations on the model to have improper bone rotations).

Any ideas?
Thank you,