I created a channel and it has 9 sub channels (I was just testing, I don't know who in their right mind would actually use 9 sub channels ). With these sub channels created, I went to Permissions > Channel Groups. I right clicked on Channel Admin and clicked Display Clients. In the left box when I scroll down and get to the channel with the 9 sub channels, Sub Channel 8 and 9 cannot be seen unless I make the whole box larger. Something similar occurs in the Channel Permissions box, some of the sub channels are invisible because of the way the sub channels appear more and more to the right.

Maybe a horizontal scroll bar would do the trick?