It's unpredictable how long it takes the officer to stamp you through; sometimes it's seconds, sometimes they take a very long look and do lots of tapping.

I assume the computer is prompting them to take a closer look. I did once get sent to the back room when leaving through DXB T1. No reason was given and I was stamped out without further ado.

@londonba2014 ... are you a frequent visitor ?