Originally Posted by
well biked
You're right, most of the time it doesn't matter. But there have been two different occasions in the last couple of years, once with a nine speed Ultegra crankset and once with a nine speed FSA crankset, where the chain would float over the smaller ring when shifting down and there was no fixing it, it simply wouldn't work consistently right. Replacing with ten speed cranks fixed both problems immediately and completely.
A 9-speed Ultegra crank (6503 triple) paired with a 10-speed Wippermann 5.9 mm chain is what I'm using on one bike right now and there has never been the slightest shifting problem so, as you say, the problem seems sporadic.