TreeTable & DragAndDropWrapper

I am running into the same issue mentioned in this post:

https://vaadin.com/forum/-/message_boards/view_message/961144

Is it a bug? If so, has anyone found a workaround?
Can the problem be resolved with a CSS styling fix?
Somewhere in the TreeTable java code?

I know the Vaadin team is busy with Vaadin 7, etc., but could someone shed a bit of light here?

Thanks!

– Jacek