Ok I've got the response from Infragistics Support posting it here:

Hello Dee,

I was able to duplicate the flashing behavior that you noted for the WebAsyncRefreshPanel during the refresh when using IE 6, although the same behavior was not visible when using IE 7 or Firefox. 
 

Thanks for the follow-up.

I can't determine your support case from the URL you posted, though from looking up your user details I believe this is case number CAS-12966-741UQG.  A Developer Support Engineer is looking into this and will contact you with what we find.

Vince, just FYI - I've submitted a support request as you suggested:

http://es.infragistics.com/support/SubmitRequestConfirmation.aspx?RequestId=907a69b2-68cb-dd11-b077-000c29df9476

Thanks.

Frederik,

I'm affraid no solution so far.
If you are able to give them an isolated example - it would be great to see the answer.

Cheers.

i have exactly the same problem. Is there already a solution or a fix ?