A separate issue, but partially related to this, is trying to track down who the donor was when the transaction doesn't make it to the database.
The following mod to Treasury.tpl will result in the Username being provided to you in the Paypal notification email.
Insert the following 2 lines between approx lines 44 and 45
<input type="hidden" name="on1" value="User Name" />
<input type="hidden" name="os1" value="$USERNAME" />
so that lines 44 to 47 look like
</div>
<input type="hidden" name="on1" value="User Name" />
<input type="hidden" name="os1" value="$USERNAME" />
<input type="hidden" name="no_shipping" value="$PP_NO_SHIP" />
This has been tested in the sandbox and provides the required result