What's happening here is a limitation of HDCP handshakes - which is High Definition Content Protection, and the connection that must trasmit a signal that verifies that the signal is being sent to a screen rather than an unauthorized peripheral.
When the two units connect, a signal is already sent and a handshake occurs, the box recognizes the transmission as verified and sends the picture. When the box doesn't receive this verification - which could be a number of reasons - the signal is still there, connected and sending, but the picture doesn't get sent until the cable box can verify HDCP.
In most cases, if you turn off your cable box and turn it back on, it will attempt another handshake and then transmit the picture.
The reason I think it's the box(es, in this case) is because there is an audio signal present, but not picture signal. The audio is passed, and no "Not Supported Mode" display. This means that the box is transmitting a signal, but not a verified signal, thus, no picture is sent.
Had you seen the Mode Not Supported or Weak or No Signal Detected icon appear, then it would indicate that the television is not receiving a signal at all. But the television is receiving a strong connected signal (by the absence of a notation). What it isn't receiving is a picture THROUGH that signal from the box - again, likely due to the lack of HDCP handshake.
My bet would be that if you turn off the cable box and restart it, the picture will appear as normal.
Let me know. I'd be interested in seeing how this turns out.