Build window pop-up whilst mouse idle for non-available buildings

On three separate occasions I've had the build window pop-up when I've not been doing anything. These have all been for buildings I've not had access to. The first two were bottomless wells, the other was a noble house. As soon as I move the mouse these screens disappeared.

Not much of a bug and doesn't affect anything, just looks weird.

For information I've got a wireless Microsoft mouse and keyboard, in case that makes a difference :confused: