Can confirm that for me it was caused by the clock on the top pager updating while using the place compiz plugin, for now have removed the clock (<special>+<alt>+rightclick remove from panel), that's stopped it popping up. I think the problem is with place plugin though and there's a bug report here https://bugs.launchpad.net/compiz-core/+bug/976032.
As for the turns-out-to-be-unrelated windows moving themselves about/jumping to the top of the screen thing that I was having that was caused by wobbly windows plugin which has a snap feature by default set to <shift> changed to <disabled> to stop.
Can confirm that for me it was caused by the clock on the top pager updating while using the place compiz plugin, for now have removed the clock (<special> +<alt>+ rightclick remove from panel), that's stopped it popping up. I think the problem is with place plugin though and there's a bug report here https:/ /bugs.launchpad .net/compiz- core/+bug/ 976032.
As for the turns-out- to-be-unrelated windows moving themselves about/jumping to the top of the screen thing that I was having that was caused by wobbly windows plugin which has a snap feature by default set to <shift> changed to <disabled> to stop.