...but not under the seat in front of the seat next to you.

Apparently that's the rule. My row was empty () so I tried to stow my computer bag under the middle seat but was told I wasn't allowed to: the bag had to be under the seat in front.

Anyone know what this is all about?

Incidentally, who knows how many of the inflight safety rules are up to the airline to make, the country, or the relevant international bodies (is it ICAO?)