On my camera there's a soft click, and it doesn't take much effort to remove the ring. But it never fell on its own and once attached it stays in place. If I grab the ring and try to move it when attached, there's a tiny bit of play (imo normal for a bayonet mount, otherwise, like with stiff lens hoods, it would loosen over time anyway). Is there dust under the ring or on the mount? Also, check that you're aligning the dot on the ring with the mark on the camera, and that the ring isn't bent.
Originally posted by monochrome What ring?
There's a ring around the lens that covers the accessory bayonet, you can replace it with other colors or with the adapter for mounting 49mm filters or the wide angle adapter.