Safari (Lion) only downloads mp4 files

I work in video production and we had begun using MP4 files (encoded with H.264 codec from Adobe Media encoder) for client review as it seems to be a higher quality/more universal format than MOVs. However, I have upgraded my laptop (MBP) to Lion and noticed that rather than streaming the files from our server they automatically begin downloading. This is not an issue in Safari on my MacPro running Snow Leopard, only the newer Safari in Lion and Mountain Lion (I have also tested on a brand new MBAir running ML). Is there something I can do to get Safari to stream these files again?

Thank you for any thoughts or suggestions.

I am running Safari 6.0.2 in Lion on my MacBook Pro.