mIRC doesn't ask for a confirmation if you use the automatic editboxes feature when pasting "one line of text", only if you use "single/multiple lines".
This is a bug and should be fixed because pasting "one line of text" while using the "single/multiple lines" feature won't actually send the message, no need for a confirmation.
This is the only problem here and you should have reported it in the "bug report" section of the forum, the option that ask you for a confirmation if there's a new line is already available, set the confirmation to 1 and you'll be asked when pasting more than one line.
Anyway, I think that the feature really should be named "Confirm when pasting more than [] lines of text", because if you use "1" with the actual wording, it means that you're going to be asked even for a single line, which doesn't make sense because as I said, a single line isn't going to be sent, there's no need for a confirmation, the number of line required for a confirmation should always be minimum 2
