Shield doesn't slow while sneaking to use in crawling state.

What I expected to happen was...:
In the test-snapshot thing Jeb posted on Reddit on June 26, 2019, it is now possible to use a shield by sneaking like in Bedrock edition. I was testing the shield in a crawling state and expected it to lower my speed.

What actually happened was...:
When I activated the shield with sneak (Lshift key) it didn't slow my speed. It did when I right-clicked to use it though...

Steps to Reproduce:
1. Put yourself in a crawling state using a trapdoor or piston (I used a trapdoor).
2. Put a shield in your off-hand.
3. Try moving while holding shift. It doesn't slow you. Now try holding right-click. The player now moves slower, as you'd expect.