Actually...they only had one missile have a problem, and that was after it burned much longer than previously reported. Not 20 seconds, not 40, but almost 4 minutes. All the other 6 of 7 missiles worked completely fine...and demonstrated accuracy that was beyond anything previously shown by North Korea...
I recommend you check this thread out: Six Scuds and a Dud - Why should we care?
Wonder how good they are at tunnel plugging?"
More likely they thought..."wonder how good the Israelis' and Americans will be at living in bunkers...or if they even realize what's coming until it will be just too late for the Infidels...Praise Allah!"
I read the thread and understand your point.
The scuds are very old technology. The failed missle is new. It failed.
The nuclear technology is new to them. A first underground test is not the time to be on a reviewing stand and wittness a tunnel plug failure resulting from failed engineering.