Vista - Offline when really not

My girlfriend and I have been having a weird problem since we started talking on Windows Live messenger almost a year ago. At random times we'll be talking anywhere from 20 mins to an hour, then it says we're BOTH offline to the other, meaning on my computer it says she is offline, and on her's it says I'm offline when in reality we're both still online. I can't find a common factor that could be causing this, and over a year there has been at least 2 or 3 different builds/versions to upgrade too, and that doesn't seem to fix it. This span of when we're both "offline" on the others computer has lasted anywhere from 5 mins, to an hour. It's getting quite annoying and frustrating somedays as we don't know if that is what happened, or the other just lost their internet connection. Anyone else heard of this problem?