Revive caching issues for multiple instances on a server?

[PBMBTM]

We run several Revive instances for different brand eletters on the same server.  With the last install of a new Revive instance, we noticed that creating an eletter ad with the same zone id as another brand's eletter caused the older eletter not to show.  So, a zoneid=1 ad on one Revive instance cause the zoneid=1 ad on another Revive instance not to show. 

What would cause this?  We even created a brand new instance and had the same problem.

Could it be cache configuration issue on the server? 

Right now we have a potential work-around to get eletters live by duplicating the banner zone ids until they are out of the range of the other brand's zone ids. 

Thanks for any insights!

[andrewatfornax]

"We run several Revive instances for different brand eletters on the same server."

Regardless of the server - what domain name do they all use? The same domain name, or different domain names?