Kenneth, we are in correspondence with Ow Factory.
The issue is indeed with mailbox plugin to some extend.
Functionality of the mailbox plugin doesn't allow user( including admin) to send PM to himself.
Therefore situation where user indeed receives a message from himself was just not considered while developing the plugin.
Since Mailbox plugin itself, Oxwall's core and Oxwall's native plugins don't create situations where user send PM to himself, we will not be redeveloping our plugin. We beleive that changes should be done within the "Report Abuse" plugin.
What we suggested to OW Factory is removing "Report Abuse" button if currently loged in user is admin.
Hopefully we will find a way around this with Ow Factory ( plugin itself seems to work perfectly other then this small glitch).