Why break standard behaviour? It is only one more press of CTRL+Z...
Note that this whole behaviour of reverting back to the characters :) when you pasted
also only happens in certain situations (depending on how you pasted the emoticons, if there was text before, and even if you have used CTRL+Z before or not, etc). Thus trying to break this standard behaviour to make it more 'clean' might actually break a lot more stuff than fixing anything.