I've seen the problem from BETA1 to HEAD
To reproduce the bug, try the following :
Create some seam-gen based project and generate-entities.
Go to an edit page, fill some data, and click on the submit button, without clicking elsewhere (the focus must be on an edited field just before submit). Instead of validation error, or adding the new data, you should get the "The conversation ended, timed out or was processing another request" message. It seems that the validation triggered by the onblur event messes up with the validation.
I have also seen the bug occuring while I was switching from one field to another quite fast (fast enough to have many validation on queue in ajax4jsf). It seems that adding <s:conversationId/> to the a:support solves this part.
Here is the snippet I currently use
<a:support event="onblur" bypassUpdates="true" reRender="cityCodeDecoration">
I tried to upgrade ajax4jsf + richfaces 3.0.1 to richfaces 3.1.0 rc2, but it didn't change anything.