Disenchant cards in Twist Cards mode

To get “Arcane Dust” I disenchanted almost all the cards from “Standard” and “Wild” that I owned 2x. That went well. But the problem occurred in “Twist card” mode. In some cases the system will allow me to disenchant the card and in other cases it will not. If not, it reports “A system error has prevented your request. Please try again.”.

The first case shows a combination where I manage to “disenchant” the card but with problems…

Let’s say that according to the filter I own 2x “Worgen Infiltrator” (Classic) and 1x “Worgen Infiltrator” (Legacy) card. Because I owned it in “Classic” twice, I disenchant it once here…it’s interesting that it disappeared both - 1x for Classic and 1x for Legacy.

Before the sell
https://i.ibb.co/tDH9syk/10.png

After the sell - only 1 copy like “Classic”
https://i.ibb.co/FnrytMf/20.png

.-.-.-.-.-.-.-.-.-.-.-.-.

The second case shows that it is offered to me by “Abusive Sergant” that I own it twice in Classic… I want to disenchant it once, but it fails, the message
“A system error has prevented your request. Please try again.”
appears.
I don’t understand - in “Standard cards” it’s unenchantable, but in “Twist Card” Hearthstone tells me it can be disenchanted…

Before the sell
https://i.ibb.co/Wv2tL3f/25.png

Sell
https://i.ibb.co/w0qjMhW/30.png

Error
https://i.ibb.co/pxmkF36/40.png

Show that in “Standard cards” it is not possible to disenchant (because it is core)…
https://i.ibb.co/8s2nwz6/50.png