I am unable to duplicate this on Dwilight in Astrum:
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.
Yep, 100%. I'm going to get someone to send me some 25 bonds, then try again. It might have something to do with having a low amount of gold/bonds overall? (don't know how it works).