Outlook 2007 – Forgetting to be default mail client

I received an e-mail from a reader that’s having problems with their Outlook 2007 beta experience. It seems that sporadically her computer forgets that it should have Outlook 2007 as it’s default, instead moving the default back to MSN.
Has anyone else experienced this. It also seems to just have started doing this, not being a problem initially after the install.
I’m curious as to if it’s something more related to MSN taking back control instead of Outlook 2007 releasing control.
To my panel of reader experts, please let us know what you think so we can help this person out.