Buy from NPC with material in stash

I really like that I don't need the material in my inventory to buy stuff from NPC, good work!

However, I noticed, that when I join the game and go to NPC BEFORE I look into the stash tab where my material is, all things are red, I can't buy anything. But after I open the stash where all my material is I can buy stuff.

I will observe if I encounter this again.