Symptom:
packets loss at group which have no switchover when we change the priority of another group

                              +--------+
                              | 7604-1 |
    +-------+    +------+-----+--------+------+------+    +-------+
    |IXIA(1)|----| 2960 |     | channel|      | 3750 |----|IXIA(2)|
    +-------+    +------+-----+--------+------+------+    +-------+
                              | 7604-2 |
                              +--------+

before:
Group 301
Active : 7604 -1  (Priority 110)
Standby :7604 -2  (priority 100)

Group 302
Active : 7604 -2 (Priority 110)
Standby : 7604 -1  (priority 100)

after:
Group 301
Active :7604 -2  (priority 120)
Standby : 7604 -1  (Priority 110)

Group 302
Active : 7604 -2 (Priority 110)
Standby : 7604 -1  (priority 100)

we send 9419284 packets from IXIA (1), but IXIA(2) received 9419267 packets.
 There are approximate 17 frames dropped.

Conditions:
The issue happen at 2 7604 (7604-1,7604-2). There are 2 group (group 301 ,302) at 7604, 
when we raise the priority of group 301 at 7606-2 to change it as a active of group 301.
we found that some packets are dropped at group 302 which has no switchover.