H.264 decoder with MFT

I have a topology that renders an MP4 file. I create a source and sink node and an H.264 decoder is inserted correctly and everything works fine in my application and also in TopEdit (Render File...).  Once I try to insert a basic MFT into the topology I no longer get any video.  The same MFT works with WMV files.  Looking at the output from MFTrace (when trying the MP4) I can see that all the nodes are connected correctly.  The output subtype from the H.264 decoder is NV12, which works fine with the other file types, but the topology can't be resolved.  Do I need to force the prefered input type on the MFT or manually construct the topology?