This can be seen in dwt-samples\snippets\menu\Snippet97.d
After the first Show event, DWT just keeps using the same menu without re-firing the Show event. The result is that the pop-up menu shows the text doesn't ever change after the menu is initially created.
This also affects my app in which I try to dynamically generate a menu that hangs off the menu bar. If I pop up the same menu twice in a row then Show doesn't fire. But if I switch to another menu and then back then it does. It appears that Hide on the first menu also doesn't get sent until the other menu pops up. I.e. if you just pop up and close the same menu repeatedly, you get one Show the first time, then nothing until you open a different menu, at which point you get a Hide for the first menu.