Failed to add to ingame mail items all goes to inventory

When I tried to add too many items to the ingame mail (limited to 10 items) from the bank windows directly, the failed to add items all goes to my inventory.

Two things that really annoys me.
(1) why the mail system limits only sending ten items at a time which is a very small number of items and I need to mail several times to send all my items to another player
(2) I am a software developer, too. These kind of bugs are just really careless mistake and you should have thought about it when you were doing these kind of simple programming.