That's possible, but I have tested it on my computer monitor and the same issues are there. The monitor is a bit older (2.5 years) but it's still decent.
I'm not sure why the box won't use 1080p with my TV either, it passes the test (the TV says it's 1080/24p) and then after keeping the settings it works for a few seconds, then flickers and goes back to 1080i. The Box still says it's running 1080p, but the TV says it's 1080i. The box won't do 1080p on the monitor either, it just goes black, so I have done the testing at 720p for it.
I don't have an OTA antenna to test with. I could pick one up, but I'd just end up returning it, and Bell wouldn't have cared (or noticed) that the picture was better anyways. The techs' eye for detail seems to be questionable.