IPMP and changing gateway

Hi,
Network guy here...I have had an issue today, whereby we changed the device that was acting as a gateway for a Solaris box (effectively changing the MAC address of the gateway - NOT the IP address)
It was in the plan to flush the ARP table of the solaris.
However...it appears IPMP was running and the interface went into a failed state once we turned off the old gateway - and even once the new gateway was up and running, arp -a on the solaris showed empty.

Strangely though we could still ping the solaris box from the gateway...

After around an hour of trying we turned off the new gateway and re-enabled the old and hey presto, everything sprang back to life...

Everything on Layer 1/2 looked fine - regarding the set up of the new gateway.
I know next to nothing about solaris and ipmp, except what I am looking into right now...
I am guessing that something in the IPMP process is holding on to the old gateway's MAC address or something...

I am also guessing that next time around we should bring the interface on the solaris down before changing the gateway

Has anybody got an words of wisdom - about how to go about this in the best fashion?

Thanks
mb