Black Boarders not being added

I frequently need to render .MTS files out to MXF OP1a using the DV 25 NTSC preset to air HD content on SD television. This automatically applies the black boarders, top and bottom. My system recently stopped doing that. Instead, where the black boarders should be, AME is stretching the image. This happens with any format that allows using the DV 25 NTSC preset (AVI, H.264, MPEG2).

I tried unintalling and reinstalling both Preimiere and Encore, but that did not fix the problem.

Any ideas?

Thanks

AME CS6 Version 6.0.3.1

Using the Adobe Production Premium CS6

Windows 7 Professional

I am using Mercury Playback Engine GPU Acceleration in Premiere Pro

My source footage is from AVCHD (.MTS) from Panasonic AG160 cameras.