I bought 20 classic packs and used the mass disenchant feature. The preview said I would receive around 1000 dust and I received around 500 dust. I then bought 10 more packs and used the mass disenchant feature again which said I would receive 500 dust and I only received around 300. Not sure what is happening.
I would say that the system is wrongly calculating the dust coming from your golden cards…
At any rate, I hope they can fix this thing soon.