A weapon that reduces my armor?!?

[Excuses]

I bought Dusk claymore Assult to play around with stat yesterday and found this.
Check our my 'Armor' please.




This is my current stat with Aegis.




And this is what is supposed to be.




This is my armor without a weapon.



And... Boom


This is the stat when I wear Claymore.



Could a dev confirm what's going on here?
Thank you.