Chrome Custom Tab does not go back to app

Question

I have a WebView that loads a HTML with links inside. Those links are opened using Chrome Custom Tabs.

Strange scenario:

1. Open Chrome browser
2. Open app
3. Press any link (this will open a Chrome Custom Tab)
4. Press the back button or the "x" button on the Custom Tab
5. Instead of going back to the app the chrome browser is shown.

[updated] The launch mode of my activity, set in the AndroidManifest, is singleInstance.

Answer 1

The problem is that my activity had the launch mode "singleInstance". Changing to "singleTask" or not having a launchMode set in the AndroidManifest solves the problem.

Don't know why is that. If you know why, I will gladly mark your explanation as the solution.