I'm sorry for the confusion. The numeric received from the IRCd is correct but I was asking the rationale of mIRC to remove the #channel parameter when it displays numeric 482 to user.
Anyway, thanks Sat for clarifying how numeric 482 is handled on mIRC. However, I am only able to reproduce case 1 whether I am on the target channel or not. I'm using mIRC 7.42 on InspIRCd and UnrealIRCd.
Please mark this thread as resolved or anything equivalent. Thank you!
Edit:
Case 1 (i.e. The following is shown in the window of that channel)
* DBoyz: You're not channel operator