Cape is jittering; movement way sharper than in snapshot 18w03b

Steps To Reproduce:

• Join any Minecraft world
• Toggle perspective mode, so you can see your cape
• Now start walking with sprint and press W+A or W+D 
• Move your mouse in the direction you're walking (it should look like you're walking in circles)
• Observe how weirdly the cape behaves

Expected Result: Smooth cape movement animation, just as it was before snapshot 18w05a
Actual Result: Cape animation is jittering

Video demonstrating the issue: YouTube Video 

Additional Information:

After a few checks, I found that the first time when the bug appeared in a game was in a snapshot 18w05a, but before that version, there was a snapshot 18w03b where everything was fine with a cape.

Code Analysis:
Code analysis by LabyStudio can be found in this comment.