Mana cost reduction effect is not detached sometimes when you replace your hand with other cards (Golden Kobold, Lilian Voss)

[Kybxd]

√- detached
×- not detached
O- invalid

Replacing card/Reduction	Renounce Darkness	Shadowstep	Far Sight	Thaurissan	Ethereal Peddler
Golden Monkey	√	√	√	√	√
Golden Kobold	×	×	√	√	×
Lilian Voss	×	O	√	√	×

(I'll upload some images later.)

However things may get weirder than the table above sometimes, such as when you have a Knife Juggler. 1.In this image the play order is Renounce Darkness-Knife Juggler-Lilian Voss, and the reduction is detached. 2.However when the play order is changed to Knife Juggler-Renounce Darkness-Lilian Voss, the reduction is not detached. (Intuitively play order is the cause, but I'm not completely sure whether there is an other internal reason.)

[Kybxd]

The reduction of Undercity Huckster is from Shadowstep. and Deathlord is from Far Sight. Play Golden Kobold.

[troggnostupidhs]

https://www.reddit.com/r/hearthstone/comments/7dkb7y/til_replacing_cards_with_with_golden_kobold_will/

Played the tavern brawl and got Fire Plume Harbinger from the goblet. Turns out that the reduction effect is being kept after transformation even though the new cards aren't elementals!

Same thing happens with [[Ethereal Peddler]] and [[Lilian Voss]]. https://imgur.com/a/UyVG4

[PattuX]

https://www.reddit.com/r/hearthstone/comments/7g0xga/golden_kobold_cthun_bugged_interaction/

Another example of this (second case in the video) with Renounce + Golden Kobold:

Before Kobold, four cards are reduced:

After Kobold just one card keeps the reduction:

Clearly it doesn't matter which minion the card is transformed into (as one Mukla is reduced while the other is not). Also it doesn't matter whether the original card was a minion or a spell. Also the Kobold was generated after all the reductions (he was on the far right in his hand), so it's probably not an issue with time stamps either... What I could imagine for Renounce is that the cards that were in your hand when you played Renounce keep the discount, but the cards that are drawn from the deck after you played Renounce don't. Might also fit Kybxd's examples above. In the second picture, Renounce was played just that turn while in the first picture it was played some time ago, possibly before the spell that transformed into Blade Flurry was drawn.

[troggnostupidhs]

https://playhearthstone.com/en-us/blog/21694420

Fixed a bug where certain cost-reduction effects, such as Ethereal Peddler or Shadowstep, were not removed when transformed by cards such as Lilian Voss or Golden Kobold.

[troggnostupidhs]

Potentially fixed if anyone feels like re-testing.