What to do when X11DRV_DIB_BuildColorMap is called with more than 256 colors?

[David D. Hagood]

I have an old copy of Microsoft's Trip Planner 5 software that I was 
trying to get to run. When I try to plan a trip, the program will draw 
the map fine, then it attempts to draw the dialog for setting up the 
trip data. At this point, the app calls X11DRV_DIB_BuildColorMap with a 
bmiHeader.biClrUsed count of 257.

Now, if I remove the code within X11DRV_DIB_BuildColorMap that checks 
for colors > 256, the code makes it past this point. It dies much later, 
after I have entered the start point of the journey.

So, now what? Is there a shortcoming within BuildColorMap, or is some 
other code misleading the app? How do I go about debugging this?