/hs cmode
[03:06:11] -qld-chat.bigpond.com- r - Registered, R - n/a, s - Secret, t - Topic, u - Channel User, v - Voice, w - n/a, y - n/a, z - Encrypt Only
It's not a bug in mIRC or a problem with CR. The mode simply doesn't exist at channel level.
Also +u is a level of host status on CR which allows /cs invite and channel memo access. You cannot /mode #Room +u with it, it is given automatically.