The caver beneath me on a pitch was passing a tied off rope by a ledge part way down the pitch. They moved their Stop to the second rope continuing to the bottom (the first rope wasn't long enough). Did the usual and tried out the Stop to check it was threaded properly before unclipping their long cowstail, but were holding onto a loose tail of the first rope rather than the one they were on. After pressing in the handle of the Stop they fell the full length of their long cowstail with a bang and a bit of a shock but no other issues.
Not above FF1.... but a particularly faffy trip with a bag in Ireby. Everything was just not quite going smoothly. One of the pitch heads I was manoeuvring the bag around prior to descending and managed to squeeze it against the stop handle (ie not holding braking end due to bag). Landed at the end of my long CT wondering how I'd got there. Yes I should have locked the Stop off until I was ready to descend. Pitch was probably long enough I'd have worked out and managed to release it in time before hitting the floor.... but you don't get that long. Have seen people hit the end of CT having wrongly threaded Stop.
I've also slipped on a traverse in Juniper and been very glad CT caught me. Would have been ok, probably.