Hi,
Budget is consumed at the time of the invoice, but if payment transfer is active (on-line or manual), then the consumption of invoice would be reduced and the consumption of payment would happen instead. Similar to reduction of commitment consumption by invoice.
In reports the distinction could be done by value type: invoices are '54', while payments are '57'. For more info on payment transfer you can consult these notes:
Note 1695556 - Main features of Customizing for onilne payment update
Note 882379 - FMPU_R: Recommendations for the online payment update
Regards,
Eli