I'm having a similar issue and neither refreshing the virtual guide nor restarting the server seems to be working.
I've manually imported several seasons of a tv show to Channels. I've given the show a custom image (4:3) and each episode a custom image (16:9). If I go to the show via the tv shows tab on my Apple TV, all images show correctly. However, when I go to the virtual channel I made filled with this show, the episodes use only uses an image automatically downloaded from the internet, not the show or episode images I added.
I've also noticed if I go to the show using the server interface, the overall custom image and episode custom images appear normally. However, if I go to the manage tab and go to the show that way, it only shows the internet download image for each episode.
I assume I am missing something here, but I don't know what! Thankfully this is not a big deal. I've just spent too much time trying to figure it out. Thanks for any help.