I have been noticing a similar situation (I don't watch 266 or 280) but do watch 284, 285, 286, 287. These four network feeds quite often are the source of programing also running on 252 CITY & 256 GLOBAL.
For example tonight Vegas was running on 256 and I was getting it on 286 as Global with CDN commercials. Other times will be watching 285ABC and when a commercial starts programming will cut out and get black screen, until next commercial and then channel comes back in but as CITY. I typically record programing and watch later so this creates black gaps in recordings. Have resorted to recording programs on 252 & 256 when I see similar program going to run on them as the 284,285,286,287's.
This situation doesn't seem to occur on the WEST feeds of the usa networks as equivalent program is not running at same time on 252 or 256. Its like when they cut the CDN commercials in on 252, 256 it overrides the USA channel completely, perhaps some kind of timing issue on commercial cut in start?
Doing a reset of receiver corrects the programming to match channel till next commercial.
This seemed to start when 252 CITY was added or last software update (occurred about same time), this only occurs on my 630 receiver not my 530. Have had 630 receiver for as long as they have been out and no such problem before now.
Recording programming on 252,256 or west feeds is my work around, but its annoying.