Mistcatch causes it valley.
Valleying dosen't mean a miscatch.
A valley is when it isn't able to make a certain element therefore preventing it from completeing the circuit. And when a miscatch ocurrs, it cannot make it through the loop, therefore it IS valleying.
It can valley in between the Loop and Cobra roll, which is not caused my a miscatch. It's just because of pure Vekoma stupidity.
They used to. Basically, what used to happen is a miscatch would occur, the train would go about halfway up the tower (or so), fall back down and complete the vertical loop, but then get stuck between the vertical loop and cobra roll. When this would happen, I presume the train was taken apart and moved back into the station.
Now, there are brakes installed at the bottom of each tower, so that if there is a miscatch, the brakes activate and the train is stopped from entering the vertical loop or cobra roll. When maintenance releases the brakes, they reattach the catchcar, the train is pulled back up the tower, and riders enjoy the second half of their ride.