[Multiple zones on 1 page - URL/cookie issue]

I have a page that loads 2x iframes, each with a separate adserver zone.

If either of the zones contain an ad with a URL target then this is placed in the cookie.

When *both* zones contain an ad with a URL, the cookie write is non-deterministic.

There appears to be only 1 place in the cookie that the url is written, but I would expect 1 per zone or some other way of differentiating them.

Have I done something wrong in configuring the server, if so what? 

I am using the iframe invocation code (so there are 2x iframes on the page), since

- some of my client devices will not support async JS,

- I want to install/configure revive centrally (not on 120 webservers) so local mode is out

- I do not want to change the many dozens of pages that already embed the iframe & are deployed on the aforesaid webservers.

Is this a supported configuration & if not then should I be looking to extend the cookie handling to multiple zones?

thanks in advance