CompuServe Messages

I'm having trouble getting R3 to multitask under OS/2 2.1. I am using the IBM S3 drivers (1024x768x256) for OS/2 and the builtin vibrant drivers for 3DS (NDI Warp10 S3 in same resolution). 3DS runs fine (I have DMPMI, int during I/O, background executtion, enabled etc.), and I even have it rendering to the Targa+ ok. But, when I switch back to the OS/2 desktop while it is rendering, the rendering stops. I can then switch back to 3DS and it resumes. I found that if I turn on VIDEO_SWITCH_NOTIFICATION in the dos settings, then 3DS will continue to render when I switch away from it, but when I switch back, the screen is black. Also, if I have it render only one frame, even when that frame is done, the OS/2 system activity monitor (Pulse) shows that CPU utilization is still about 100%. Also, if I have it render several frames, it will render only the first one. It won't save any files either. To reiterate, everything works fine as long as I don't try to render in the background. Is anybody getting 3DS to render properly in the background under OS/2?