the problem is that the refs didn't seem to know the rules
According to the courier mail (i know ... but) in that situation it should not have been a drop out, but a turnover, giving the Tigers the ball back
It was a mutual infringement, which is basically a catch-all for when something weird happens, such as the ball bursting, the referee blowing his whistle accidentally, a dog running on the field and tripping someone etc.
If something weird happens, and it irregularly impacts the game, it is pulled up, and scrum is awarded at the point of the infringement, with the loose and feed going to the attacking team (territorial position). Unlike other scrum infringements (knock on, forward pass etc) this one does not turn into a changeover after the 5th play the ball.
So Newcastle scrum 25m out.
Tony Archer has confirmed that this could have been an option - but has put the caveat in, that the referee is the sole judge as to whether the game has been impacted. So essentially, the referee either didn't think the game was impacted, or he didn't know the rule.