dynamicContent controls unfortunately do not work with partial updates, only with a full reload of the page. I tried the same some months ago and it didn't work for me, too.
I used the workaround to put my pieces of "dynamic contect" in custom controls and use their rendered
property to display them depending on the state of a sessionScope variable.
It's not perfect since the XPages engine always has all content of all custom controls in it's tree, but it's ok for medium complex applications.