The "was" operator on the assignee field does not return results for inactive users

When running a query with "assignee was bob", if bob is a inactive user the query returns nothing with the following error message:
The value 'bob' does not exist for the field 'assignee'.

But if bob is reactivated the query returns results as expected.

This is also happening to the 'was in' operator, when the user is inactive and hasn't been assigned issues, like shown below:

assignee was in (usera, userb)

If usera, for example, is disabled and hasn't been assigned issues.