[Exim] Colon in PW & SMTP AUTH

I have come across an issue with having a password which has a colon in it.

example: tmp:45!

If I have the password set this way SMTP AUTH does not work. If I change the
password to tmp45! instead it works fine.

What is going on? Is : just a bad character or is there a bug in Exim?

I'm running Debian unstable with exim v. 3.33 #1.

Thanks
ian