Mobs can float for a short while when hit while on top of slabs

Mobs will sometimes float when hit, when they are above a bottom half-slab. A demo video and the used world can be found in the attachments.

Steps to Reproduce:

Build a 1x1 hole with the following blocks:

W
S
A
A
HS

W=flowing Water
S=Sign
A=Air
HS=bottom half slap

Next, let mobs down that chamber and hit them. Some of them may float occasionally.

Expected Result:

• mobs just fall down as expected

Actual Result:

• mobs remain floating for about a second