This issue can occur if the HDMI output of your Set-Top box is set to 720p. The 720p output signal can cause the channel logo to flicker after the TV is left for a while, which will then cause the logo to remain displayed.
To avoid the issue, from the AV setting of the Set-Top box, change the output signal to 1080i. The issue will not occur with the 1080i set as the output. For assistance with how to change the output signal on your Set-Top box, refer to the manual supplied with that device.