I tested this myself, and yes this is exactly what happens.
Memory tag to test:
Toggle the tag and the alarm appears in the table:
Ack the alarm:
Check the system tag:
Everything is as expected so far.
However, when I shelve the alarm, clear it and re-activate it you can see that it does not appear in the table but the Active and Unacked system tag counts the alarm.
I would say that the Active and Acked and Active and Unacked count should not count shelved alarms because they are not "active."