A curious observation. I was watching a YouTube video in Browser for about 10 minutes and when finished, I navigated to another site (TMO, for those curious ones ). Then I decided to close Browser, which I always do by closing all open tabs to avoid Browser opening them again the next time. I only had one tab open anyway. But, what would you know, tapping on the square in the Browser bottom bar did not bring the list of tabs as expected. Oh no. It brought the unlock screen where you need to tap your PIN.

If I understand it correctly, my screen timed out while I was watching the video but the video playback prevented it. But some flag was set somewhere that the screen had timed out and so the unlock screen was shown at the nearest opportunity.

I have seen it happening on other occasions with other apps that keep the screen alive, such as Pure Maps during navigation. In such cases, navigating to the home screen is greeted with the login prompt. Annoying, as it does not match the user's expectation (the screen has never gone dark, why on earth do you want me to unlock it?), but at least understandable. But this? I never left Browser. Navigating from YouTube to TMO did not prompt me to unlock the screen. Only opening a different view in Browser (the tabs list) did. As if that counted as trying to switch to another application. Positively weird.