I honestly do not think it has to do with their OTA. they were already sending a 720p feed to BEV before OTA launch which is by the way 1080i. I wonder if the simsubed US Network also has had the same problem. I would recommend you to also contact Global and BEV and ask them. Last weekend I set up an indoor ear-rabbit (VHF only) antenna for a friend and his family at their new aptm in Toronto and they watch mostly Global HD and CityTV HD OTA and just this morning they told me how impressed they are with the picture quality in their first week enjoying free OTA HD television.
It could be BEV - Global link equipment as well, not only their respective broadcast equipment. I beleive I recorded Numbers on CBS HD (simsubed last nite by Global) I will have to check that later.