SymSpec,
We have tested this process and see below for our results.
When we click isolate a endpoint from the ATP console the endpoint see these results.
After rejoining the endpoint from the ATP console we get this:
As you can see HI changes the location when it places the endpoint into isolation (Default >Quarantine) and when we rejoin it HI changes the location back to (Default)
Please let me know if this answers your question.