Clock doesn't respond to hover or click

In a recent update (I'm not sure exactly when, since I just noticed this issue yesterday) the clock in the tray no longer responds to hovers or clicks.  That is, hovering my cursor over the clock no longer displays the date in a tooltip, and clicking the clock no longer brings up the calendar.  Exiting from 7+ TT resolves the issue.

I'm on Win 7 x64.