I just got one character up to level 20 so I started a new character.

I'm looking at the customization screen and every hat/shirt/etc is already unlocked and I'm still level 1.
It seems like the unlocks carry over to new characters. Whether this is intentional or not, I don't know.

Intentional, and everything but the challenges moves from char to char.

Pretty sure it's intentional. So long as you maintain a high level character, new characters gain access to all weapon attachments and aesthetic options.

When I read the title I thought you were talking about the archetype 'the bug'!
I'm glad this is the way it is.