Plan warnings stay until the plan is re-loaded

In an Iteration Plan, on the Planned Items tab, if there are
warnings/errors (like an item is past its due date), a warning is
displayed across the top bar of the Plan window. I can click on the
warning and get the details. However, if I fix the problem (or it has
been fixed by another user), the warning doesn't go away, even when I
"refresh" the plan. (At this point, when I click on the warning, the
detail box is empty.) I have to close the plan entirely and reopen it
in order to make the warning go away.