5.1 export ->visio<- visio import loses data

[richard williams - IoDynamix]

I've got Omnigraffle 5.1 beta on my imac, working on visio files for  
customer configs. When I add a visio stencil image (like the IBM blade  
server chassis,) all the data comes in and the drawing looks good.  
When I export it to visio XML, then open it with Visio 2003 or 2007,  
It seems like some of the layers (or detail) in the chassis dropped  
out during the import. Can anyone help me understand what I need to do  
for good results?

thanks!