Testfor OnGround:1b after teleporting causes check to always output true

The bug

If you have a command that is constantly teleporting you, with a command that constantly checks if you are OnGround:1b after the teleport, the OnGround check will always output as true.

How to reproduce

1. Repeating command with a constant teleport to X Y Z
2. Chain command after teleport running

   /testfor @p {OnGround:1b}

   1.13: /execute if entity @p[nbt={OnGround:1b}]

3. Comparator out of chain command
4. Run system (start the teleport command FIRST then start the testfor command) to see that the testfor will always be true, even if the teleport puts you in the air. You can check with OnGround:0b to see that the output will always be false.