PowerPivot bug?

I ran into an interested thing this afternoon when working in the PowerPivot window.

When the PowerPivot window is maximized I see the following:

So it seems all the tables (which are there) are visible.

But when I restore the window, so it is not longer maximized, the blue triangle reappears and the rest of the tables are accessible again.

I believe it is a bug, but has anybody noticed this before?

I'll try and check this with MS later when I get the chance.