Armor pasive adds zero armor

[AngryLucas]

First, I don't remember exactly but I had about 7750 armor.

Then, I made respec and armor went down to about 7500 (before giving 5 points to Durable).

Thirdly, I put 5 points to Durable but armor stayed about 7500.

Then, I made respec again and ¡surprise! armor went down to about 6500 ¡¡¡1K armor less!!!

Finally, I put 5 points to Durable and the armor is 6928 -> This time Durable works but I have lost 1k armor.

To sum up, after doing my original respec, I have 6900 armor instead 7759 armor.

How is it possible that Durable works differently in different respecs?
How is it possible that after all I lost 1K armor?