Underlying form updates before existing form is closed

I'm having an issue where controls in a calling form are being displayed
before the called (topmost) form is closed. Here's what happens.

1. The user goes into a "user ID" setup screen to choose the user.
2. A form is displayed that shows some user information including password
textboxes. The user enters the information and presses [Signature].
3. The user sees a signature screen, signs their name, and presses [Next].
4. The user enters a name to identify the signature and presses [Save].
5. At this point, the password textbox is displayed with the stars in the
field. Then, the screen in #1 is displayed.

What is causing this and how can I keep it from happening? It seems like
the system does this quite a bit both going into the next screen and coming
back out, but mostly when it's closing two or more screens at the same
time.

I'm using CF1 and there's no SuspendLayout() method to stop drawing the
screen. I'm not even sure if this would solve the problem.

Is there a way to fix this, or does my customer just need to deal with
this?

Specs:

a) CF1
b) Visual Studio .NET 2003
c) C#
d) WinCE 4.2
e) Pocket PC 2003

Any help is appreciated.

Thanks,
Kevin