Several times I have been on a flight with my parents. I use a mobile boarding pass while my parents use a paper one.
At the boarding gate, they take my parents' paper pass and scan it. But for me they ask me to scan my boarding pass.
Are airline crew instructed to ask the passenger to scan his boarding pass if displayed on a mobile device?
I have a feeling this is true as if the person drops the phone the company don't want to be liable for cracked phones.