[Shaders Bug] Weird motion blur glitch on any shader

[RacingWatermelon]

Turning on motion blur for any shader in all of the optifine 1.15.2 releases causes the arm to blur and glitch out. This did not happen on optifine 1.14.4.

[rre36]

This is a (well) known issue affecting shaderpacks that use a specific method to detect the hand due to a bug in OptiFine for 1.15.
Related: #3646

[Speeskees]

Same for me, I've had the issue since the first shader-compatible release. Walking also messes around with the hands, especially backwards.

[sp614x]

Duplicate of #3646.
Fixed in pre17.