Mystery of the disappearing panel

I use auto-hide for the panel, but sometimes it gets stuck in the 'visible' position and won't disappear. This can be dealt with by toggling the autohide feature off and on again, which usually fixes it. Rather more difficult is when it doesn't auto-appear after hiding itself. It only happens occasionally, and it's hard to determine exactly what causes it, but there could be a correlation with cpu activity, including a lot of USB (pendrive) I/O. Once it disappears, there's no reliable way to get it back other than logging out and in again. Does anyone have a better way? This is 4.4 but the same thing has also happened with every previous 4.x version. poc