[IPMP] Physical IP address used when an interface switches from active NIC to standby NIC

In an IPMP setup, when the floating IP address is moved from the active to the standby NIC in case of problem at the router site; is it expected that for some time the standby physical IP address is used?
See output below for more information:

test-1# snoop -r -d bge2 port 5060
Using device /dev/bge2 (promiscuous mode)
10.10.70.121 -> 10.10.70.1   UDP D=5060 S=41087 LEN=14
10.10.70.121 -> 10.10.70.1   UDP D=5060 S=41088 LEN=14
10.10.70.121 -> 10.10.70.1   UDP D=5060 S=41089 LEN=14
10.10.70.121 -> 10.10.70.1   UDP D=5060 S=41090 LEN=14
10.10.70.121 -> 10.10.70.1   UDP D=5060 S=41091 LEN=14
10.10.70.122 -> 10.10.70.1   UDP D=5060 S=41092 LEN=14
10.10.70.122 -> 10.10.70.1   UDP D=5060 S=41093 LEN=14
10.10.70.122 -> 10.10.70.1   UDP D=5060 S=41094 LEN=14
10.10.70.122 -> 10.10.70.1   UDP D=5060 S=41095 LEN=14