So, the fact that sidekicking being "hit or miss" for me is a bug?
To be clear, I don't team very often. Without the number of character slots available in CoH (I'm on a silver account in CO), I have a decent range of character levels, but I don't always have a character within a level or two of the team leader, when I even team. I've probably teamed a few dozen times, and I've only had the dialogue box come up a handful of times. Probably a half-dozen of those teams were "contrived," dual boxing to try to find a way to "force" the dialogue box to come up.