When, for example, I am in the Gmail app reading an email with a link to a movie on IMDB, and I touch the link to open it, the IMDB app launches and displays the correct thing, BUT the IMDB doesn't launch as a separate app! When I display all running apps, this is what I see:

Screenshot (click for larger image)
IMDB "overtakes" the Gmail "window", and now I can't use both apps at the same time. I want the IMDB app to be in a separate "window". How to do this? Same thing with opening a Youtube link from Chrome, or any other app combination...
The device is Nexus 7 (2013), with Android 4.4.2.