wait_fences: failed to receive reply: 10004003 and navigationcontrollers in tabs

Question

I'm having a heck of a time with the

 infamous wait_fences: failed to receive reply: 10004003 

console message on an iPad app. I've searched Stack Overflow in vain for a solution, but most answers seem to be talking about textfields and the like.

My app has four tabs. Within each tab is a navigationcontroller. At launch, each tab has a view that displays a grid. (MMGridView by René Sprotte). When you click the grid, it displays a new grid by pushing onto the stack the usual way:

[self.navigationController pushViewController:c animated:YES];

My problem: on the first view of a particular tab, I can rotate all night and day and the view rotates nicely. But, once I've pushed another one onto the stack, I get the dreaded wait_fences console error upon rotation. And there is a big pause. Then it rotates. If I do this a couple more times to the same grid, I can cause it to crash.

Clearly I'm missing something obvious. What gives? How can I fix this?