"Automatic Payment Forward" - what the hell?

[tereque]

I just bumped over (in my eyes) strange behaviour in the relation 
between Invoices vs Payments

For example there is an invoice that has listed a payment (when saying 
'show payments' in the print preview) that never has been booked for it.
When looking deeper into this I have found payment in my a/r which are 
called"Automatic Payment Forward" .... There had been overpayments of 
other invoices of the same customer (and of the same job). Maybe this is 
somewhat related?

But it seems to be a little random and not really predictable ... can 
somebody explain the mechanics behind this?
Maybe there can be some benefit of this even if one just new exactly how 
that works.

thanks as always ....