AssertionError in Table

According to
I set the -ea VM parameter to enable assertions during development. This showed an assertion error with my code at

According the comment it should only happen if client and server are out of sync.

I’m using a Table (with multiselection enabled) together with a BeanContainer. The BeanContainer is updated every few seconds. Changing the selection after an update of the container lets the assertion fail. If assertions are disabled I don’t see any obvious problems though. How can I make sure that client and server are in sync?

BeanContainer is updated in a background thread? Is the code wrapped in UI.access?