Two cart incidents during many years of flying as SLF
Once (early 1970,s in 707) watched a trolley take off vertically complete with Cabin crew during unannounced and presumably unforeseen CAT which landed on a seat, fortunately unoccupied, although it did break the arm of the passenger in adjacent seat. The cart was being used to clear meal service so presumably a little lighter than normal. There were a number of other flying people and objects in the incident which were "broken" but we carried onto Paris anyway !
Have only seen one runaway cart incident and that was on Kenyan Airline, and I think the break was not fully applied, as it shot off to meet its friend in the galley half way down the A/C accompanied by some vocal Swahili.