Rounded corners disappear in MultipleDetailViews sample code

I'm using an UISplitViewController to show multiple detailViews depending on the selection in the root view. To get 开发者_开发知识库started I used the MultipleDetailsViews sample code.

When I rotate the iPad to landscape mode and select a DetailView on the RootViewController the inner rounded corners (next to the separator between the Root- and DetailView) disappear.

This happens in Apples sample app out of the box!

What can I do to stop the inner corners from disappearing?

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Looks like iOS 4.2.1 fixed the problem in the simulator and on the device.