odd problem with watsup and VB6 application with modal dialog

[Grumman]

For various reasons, I've found myself in the position of needing to 
automate the operation of a small VB6 application from an external 
process. After a bit of searching, I found watsup, and it has fit the 
bill nicely, except for one problem.

Roughly, I have a script that fills in a field, sets a combobox, then 
clicks a button via clickButton. At this point, the python interpreter 
hangs. The only thing I've been able to identify as different about this 
form is that it is set as dialog-modal.

I've managed to work around this by adding a second python script that 
contains just enough code to click the offending button. I call it via 
os.system('start other.py') and it starts in a different process, clicks 
the button then hangs.

But the main script continues on to fill in the following form, and 
click another button. When the VB app returns to its starting form, 
destroying the other form instances, the hung interpreter ends.

This works, but it is quite the ugly kludge isn't it?

Is this a normal behaviour for watsup with modal windows? Is there a 
saner way around it?

I should point out I spend my days in the midrange world, so I'm largely 
ignorant of the vagaries of the windows API and such.