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When you down shift, instead of falling completely on the small ring as you pedal round, the chain sticks to (or gets sucked by) the big ring in one point, and get jammed in the front mech if you don't realize what's happening early enough. Can lead to front mech totalling. It sucks.
Not sure if clutched mech would help. Fwiw I've tried running a longer and shorter chain (and also playing with the rear mech b-screw to have even more tension) and that didn't seem to change much.
If anyone wants to give it a try I’ve got a 48/32 Zayante that’s now unused. Comes with the problems mentioned above though!