Guild Wars 2

I opened 2 boxes of bladed armor on my thief and took heavy armor and put it in the bank for my warrior.

Usually armor from boxes comes out account bound, but this time it was soulbound? What do I do with heavy armor soulbound to my thief…

Unlock the skin and xmute it onto your warrior.

Eh, yeah. Thats not the issue there. Those armors are exotic, I wanted to use them for the stats.

You can try to ask support (Top of the page → Support → Submit a request) if they can send you a replacement.
They are usually really helpful if you ask nicely.

I did same thing.. IMO should be soulbound on equip.