If the mac version is like Windows, there is a row of icons at the bottom of the call screen. One of them is a chat bubble, which opens a chat with the caller.
EDIT: I should read the article - it has this in there.
It's very similar, and having barely used the Windows version (a long time ago) I got burned with the same things: hanging and sending/chatting while on a call.
I guess if everyone is complaining, it ceases to be a problem and becomes a feature :-)
EDIT: I should read the article - it has this in there.