Stops responding after returning to previous screen

I am developing a channel, using the roListScreen component. I find that when I go down one level, then use the back arrow to return to the previous screen, the system no longer responds to my button press when I attempt to go back down to the next screen again. I can continue to go up the stack, but not down. This happens on levels 1, 2, and 3. I can go down, and back up, but never down again unless I exit and come back in.

Can anyone offer insight on what I might be doing wrong here?

I am using the same code in each function, so I am wondering if there might be some sort of variable scope conflict happening. However, it is my understanding that the variables within a function are scoped to that function, so I don't see how that could be the problem.

Do I need to use unique names in each function?

They all currently look like this:

    screen = CreateObject("roListScreen")
    port = CreateObject("roMessagePort")
    screen.SetMessagePort(port)
     .
     .
     .

If anyone can offer some guidance here, I'd appreciate it.

Thank you,

Kenny