Problem changing menu text

I have an application that uses a notify icon. When the user right clicks I display a context menu. One of the menu item's text should be toggled between two text items each time it is clicked. The menu item Click method has the following code:

timerActive = !timerActive;
menuStartStopTimer.Text = timerActive ? "&Stop Timer" : "&Start Timer";

I have verified (by setting a breakpoint) that the method does set the correct text but it always displays the initial setting. How do I get the text to change?

Thanks in advance,
Hal

Additional information:

If I change the text before the context menu is displayed, the menu shows the changed text. Once the menu is displayed, the text won't change.

Regards,
Hal