NUI + iOS7 - no background color for buttons

I'm experiencing some weird inconsistencies with NUI under iOS7: some buttons doesn't appear to render with a background colour.

The app consists of a navigation controller. The buttons within the root view appears to be working just fine:

A few segues later, there is an (at least to the Interface Builder) identical button, albeit with a different appearance all together:

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I note that the navigation bar is inconsistent too in its rendering:

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.... yet sometimes:

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Do you guys have an idea what I might be doing wrong?

Solution

I decided to use UIAppearance instead. NUI is not compatible with iOS7 at this time.