I've never seen a leaky detector leak on the Ka band - most of them are too old to even know what Ka is. I pick up plenty of those cheapies (and it makes me want to get out of my car and tell the owners to turn them off, since they are probably so cheap that they aren't useful in the first place) and in this case it was a) broadcasting on Ka and b) started about 30 seconds after the guy pulled up behind me and stopped after he passed. Those together suggest that it was deliberate and not just a cheapo detector.