the 10 speed chain can get between the chainrings and jam. The inside measurements are the same as 9 speed chain, but the outside measurements are around 10% narrower. I tried this on an XT crank and it worked for a while, then it got jammed.
not sure I follow this - you are saying you have had the 10 speed chain jam between the crank chainrings (either between big and middle or middle and granny ring) in a 10 speed chainset?
I am using 10 spd chain on 9 speed chainsets and have not had that happen (yet) plus I would expect the 10 speed chainrings to be a tiny bit closer together so there ought to be less space between them for any chain jamming. ..... or am I misunderstanding?
..... 'nother question - presumably since 10 and 9 speed cassetes are same wdith, the middle 10 spd chain ring is in same position as a 9 spd so there are not nasty chain angles introduced? (Q factor stuff)