Help! Desperate! Messagebox causing form to disappear

I have two forms on screen, let's say the order is form1 on bottom, form2 on top. Form2 has focus and calls a messagebox, when the messagebox appears form2 disappears, and when a selection has been made in the messagebox form2 reappears. I can get this to not happen by minimizing form1 before calling the messagebox or by hiding form1.

This is very odd and I have never had a problem like this with a messagebox before. I'm really stuck. I know that I could problably write a routine to keep form2 on top with SetWindowPos, but I want to know why this is happening. Anyone have any ideas?