Read original post at Niko Vrdoljak's Blog
Do you know what is easiest way to crash someone’s WP7 application? Just quickly double-tap it’s “Rate my app” link or button. Marketplace Review page will display, but when you go back to app, it will disappear because it crashed.
Of course some app’s has this issue properly resolved, most not, but what happens when you double tap button or link that starts any kind of WP7 Launchers? Simply, your app will try twice to launch task, but second launch will throw “Navigation is not allowed when the task is not in the foreground” exception, because your app is not anymore active on phone.