Bug: only user image appears when I press the Windows key on the keyboard

All of a sudden, only my user picture appears when I press the Windows key on the keyboard - the rest of the Start menu is missing (to be more precise: this happens the first time I try to open Start menu with keyboard after it was opened with mouse; if I try it two or more times in a row, the only thing that happens is that the active window loses focus). My taskbar is set to auto-hide, and I'm using a high-contrast theme, if that matters.