Help Can't seem to un-install K-9

[vpcocco]

I don't want to have use any root or sysadmin option for this but:

Something's happend to my K-9 mail app where it wont delete message from the server when I delete on the device. So I've decided to just un-install and then re-install.

I go to Market - My Apps and hit the 'un-install' button but K-9 doesn't seem to go away.
How am I supposed to get rid of this app?