I once had an occasion when an aircraft not only lined up without a line up clearance but crossed a red stop bar in order to do so!! What was going on there I still ask myself.
As far as the principle of crossing red stop bars goes, it is definitely a no no as far as I am concerned. In fact Mats 1 now gives specific instructions that if you have a stop bar that serves a runway and cannot be lowered, you are supposed to either take the taxiway out of service or arrange for a vehicle to escort the aircraft over the stop bar! Never quite got to grips with that one bearing in mind that most aerodromes usually reserve stop bars for night or LVP operations - introducing yet another potential for conflict onto the runway!!
