Clicking OK on "Time Spent can not be zero" error window does not close window

Steps:
1. open the Task Board
2. click the edit button to update work log hours
3. enter a reestimate but do not enter time spent
4. click Add
5. when the error window opens, click OK to close the window

Observed:
Clicking OK does not close the error window. You have to refresh the screen to close the window and whatever you entered is lost.

Expected:
Clicking OK should close the error window.

NOTE: This problem exists in both Firefox and IE7.