Bas,
It seems that the switching between tabs and the refresh of the grids listening to other grids is a bit 'buggy', so you could try to submit a support call.
As you are saying that the grid is available on every tab page it could be an option to change the layout and place the grid outside the tabs. This would also enhance the performance of the form as the data does not have to be retrieved every time the user switches a tab. And this circumvents the issue that you are experiencing.
I hope this helps.