First of all l suggest you not to use goto ever again (Not only in mirc scripting but in any programing language)
Goto=if elseif etc
Codes with goto inside are always very hard to read
Second .Your code can be written in a single line
For me it works fine .I just added F4 { kb $snick($chan) }
i tried /kb nick and through popus and it was ok
Just add this line
if ($1) { do your code }
else { echo .... }