Trade site bug

Occasionaly i've got a game breaking bug in a trade site. The bug is that i cannot choose quantity of tradeable item. This bug happened out of blue and not have been preocupied by restarts of my PC.
It asks me to "use sliders above to generate your offer in the seller's language". I have the needed amount of currency, but can't choose any. Also i can't PM directly to a seller.
Is there any solution to this?

https://imgur.com/a/1HdaKAY
some proofs

Solved!
Problem was in incorredct stock of a seller. Somehow they used to post an offer with insufficient item. GGG team have my respects!