Apps don't launch in a separate "window"
That's not a bug, it's a feature. It's called the "Back Stack".

The idea is that you perform a single task, like reading e-mail, and all Activities, that it's what "windows" are called on Android, are grouped together on the task's back stack.

If you want IMDB "in a separate window", that is as activity of a new task with its own back stack, you can simply open it from the launcher by selecting the IMDB icon.