Error when use flipview with navigationcachemode is required?

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C#

XAML

Windows-Phone-7

I have Windows Phone 8.1 project . MainPage has a FlipView. FlipView has 2 FlipViewItem. I want to the MainPage will be NOT reload when I back from another page to it, So I used NavigationCacheMode = Required. And it's worked, but it has a other problem.

First, I swipe to second FlipViewItem.
Click to "Navigate" button to go to next screen.
In next screen, click "Back" button to back to MainPage.
And the problem is : Touch in the screen, the First FlipViewItem to appear and disappear when I touch out.
What's happened? And How can I fix it?


Thank you very much.

What I have tried:

Sources : https://drive.google.com/file/d/0B7fhq7a2URELenJuVm8xcnowMlU/view?usp=sharing