I am unable to duplicate this on Dwilight in Astrum:
10563 gold, 0 bonds
deposit 50 gold
10513 gold (50 bonds)
Send 25 gold
10513 gold (25 bonds)
Are you sure you didn't try to send someone 5 or 10 bonds? There *are* bank fees for those small transfers, and they are clearly defined on the bank page.