" why sometimes the window will close immediately? "

in my application, sometimes when i do something like the time when i select a certain menu and invoke it for certain operation, the application's window will close immediately.
my problem is, when i select an object and then select the delete menu, the window will close immediately. however, if i invoke the same operation through the delete key from the keyboard, the delete operation can be done properly. in the OnKeyDown(), i call the OnEditDelete() to do the operation.
how can this happen?