Changes made in XAML Designer showing in application only after Rebuild

Question

If a start Debug after adding button control in Designer there is no button in application until I force Rebuild of the XAML project.

There is just one test project from VS templates (It means the error occurs in both real and test projects) Application for Windows Phone 8.
XAP is not read-only.
Clean Solution don't help.
Other application (XNA) on the same phone Emulator works fine.

Answer 1

I have created new empty project and it worked fine. Maybe my previous test project was influenced by something. It was my fault.
Remember: Computers don't do mistakes unlike people.
Сonclusion: New empty test project is a very usefull way to understand the reasons (or solutions at least) of bugs.