Thanks Xman and all for the info. My Karoq is a manual and I was in a queue of traffic with EPB on and car in gear with clutch depressed so maybe I had slightly released the clutch without realising ; I'll try to replicate later ! As a matter of interest, I did find a report on Autoinsider.co.uk that there was a recall for Karoqs in November 2018 relating to cars built between 1.7.17 and 31.8.18 for what appears to be this same problem : "Parking brake may be released inadvertently when disengaging clutch", recall ref 45H5. It required a software update to fix.
Anyway, car is in local dealer week after next so maybe then I'll get clarification.