Menu formatting in the dashboard

I’m having trouble with the formatting of the menu in the dashboard (not the front end). Sometimes the menus look like this (correct):


and sometimes the menus look like this (incorrect):


I haven’t been able to link it with a particular browser, platform, or situation, although I suspect it occurs when there is an error of some sort - the CSS doesn’t finish, or something like that. When it happens, I haven’t found a reliable way to get it to stop (reloading never works).

Any help is appreciated…