Here is an example from today's early games.
There are 3 live broadcasts:
Baltimore Orioles - Baltimore Orioles @ Toronto Blue Jays (MASN)
Boston Red Sox - Tampa Bay Rays @ Boston Red Sox (NESN)
Toronto Blue Jays - Baltimore Orioles @ Toronto Blue Jays (Sportsnet)
All three streams are active and viewable on the MLB.tv website, but when viewing them through Channels, only the NESN and Sportsnet feeds are working. When trying to watch the Baltimore Orioles broadcast, I get the "This stream is currently Off-Air" message.