Rename a mob (I used a villager) to lets say, Bob.

Try to remove the name by using

It won't change the name.
Edit:
I've been told that setting the name to " " will remove the name, but not the nameplate.
This should be corrected regardless, since I assume it is not working as intended.

White-space trimming should be turned off, and rendering the name plate should check for both CustomName tag existing, and it not being blank.

The only way to correct this is to kill the mob, and spawn in a new one, which is very inconvenient if you've spent a while trying to fuss with other tags to make your mob display right.