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sup7L-E unicast flooding:ARP refreshes but MAC doesnot

I have two 4507 switches configured HSRP, 45-1 is the active gateway of vlan2. Last week we found vlan2 was sufferring unicast flooding which was explainded by case#8 at this link Then I changed the mac aging-time to 4 hours as the link suggests.

The problem seemed resolved. But after 20 hours, the problem reoccurred. I checked the ARP table and MAC table, the ARP entry of the IP address whitch caused the flooding updated 3 minutes ago. But there was no MAC entry for  the MAC address of this IP address!!! I pinged this IP address from 45-2 so the entry was established. After the weekend, I check the switches this morning, it reoccurred again.

In my opinion, the MAC entry must update as soon as the ARP entry updates,  then how could this happened again and again after the MAC aging-time was changed the same with ARP timeout?

Is there same case?Could anyone help?

The engines are SUP7L-E and the IOS is cat4500e-universalk9.SPA.03.04.00.SG.151-2.SG. TAC found no bugs by now.

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