Nickname format does not work as expected

[Nicolas Tsagarides]

I am using the Alternate Lines theme and using this custom nickname format "%@%-12n: " (without the quotes) to have each colon sorted.
The problem is when some nicks have a character prefix and others do not.
Here is an example: http://jsbin.com/pohudosenici/
When BenbopMint or Jdbye|Tabtop talks, his/her/it's colon does not line-up with the other colons of the other nicks