ONOS changes group state from PENDING_DELETE to ADDED if device takes some time to delete the group.

I have a test device which take some significant amout of time to delete a group due to some reason. I did the following to produce the issue at ONOS:
 
1. Added a group though onosproject rest app to that device.
2. Waited for the group's successful addition. Group state transition happend from PENDING _ADD to ADDED.
3. Then deleted the group. The device received the request. It was in the process of deleting the group, meanwhile the group_stats/desc messages had come to device. The device replied with the group info since it was still not deleted it. In ONOS, Group state was PENDING_DELETE for some time then again moved to ADDED.
4. The device finally deleted the group from datapath. But ONOS re-issued the group add message to the device.
 
The above behavior is not true for flow delete.
 
It seems like a bug in ONOS.