Here is the fix. Please beat on this.
http://neuron2.net/dgavcdecnv/NVbeta5.zip
There are two changes:
1. Now has D3D9-less operation. That should be more robust and perform better on low-end adapters.
2. Fix for the stream truncation by half with DGMPGDecNV and DGSource(...,deinterlace=2).