I'm not sure if it's non-compliant or against specs to have the ts without a PCR. If so, then Discovery and any others doing this are to blame. Probably have as much luck getting them to admit and fix as it is to get Microsoft to fix the Windows Explorer issue.
Regardless, the issue is because of how Windows is parsing the file to look for stats like duration, dimensions, frame rate, etc. I don't know how Windows does the parsing.
All I know is if I remux with ffmpeg (ffmpeg -i "filename.mpg" -c copy "filename.ts") or save with my video editor, they both create the PCR that is missing and put it in the video stream PID where it belongs. (Not enough packets in an audio stream for the PCR)