TreeTable + GAE problem

To whom it may concern…
I am using TreeTable addon for a school project. It is backed up with the BeanItemContainer that implements Container.Hierarchical, which is filled from the BigTable via JDO. I want to be able to add beans into the tree (after mouse click or some external events from the other components). So if I want to add another bean to the tree, I just create a new JDO in the database, convert it to some DTO and call addBean method of the container. Everything works fine if I create the hundreds of beans programmatically and add them to the tree before the first render. But if i start clicking the addButton relatively fast, very soon I get the following exception:

Sometimes it happens after tenth creation request, sometimes - after the very first one.
It occurs also when I have a bunch of the beans in the container and start scroll the tree up and down fast. I’ve spent a lot of time trying to figure out, what causes such a failure, but all in vain. Has anybody met something similar or probably knows the workaround to such a problem?