In any case, I think it *should* show the last line in the active editbox regardless where mIRC's running that command.
It could be considered a sense of logic. I myself disagree.
Normally, when a user manually enters "/", of course you want the result to be in the active editbox, but since you can only manually enter it in the active editbox, that's a non-issue.
If a script runs "/" in a specific editbox, it feels natural to me, that the effect should occur in that specific editbox, and not whatever editbox the user happens to be selecting.