Windows Live Hotmail account is POP but acts like IMAP - why?

I have this account setup in Windows Live Mail (WLM) (version 2000). It is setup in WLM as a POP3 account. But, if I send a message via WLM and then sign in to the account via web browser, I see the sent message there. This is clearly IMAP behavior, not POP3 behavior. A normal POP3 account would result in a message sent via WLM being captured in the "Sent items" folder in WLM but not synchronized to the account on the mail server and then appear in the online "Sent" folder.

Am I thinking clear here or has my brain encountered some fog? Is this a unique Microsoft Windows Live Hotmail behavior?