Collectible Card Game Headquarters

Describe the Bug:
When a player activates Chandra, the Firebrand's -2 ability and then casts an instant or sorcery while a Lodestone Golem is on the battlefield, he/she is asked to pay for the copy.

Which card did behave improperly ?
Chandra, the Firebrand or Lodestone Golem

Which update are you using?(date,name)Which type(Duel,Gauntlet,Sealed Deck)
JOU, duel

What exactly should be the correct behavior/interaction ?
Lodestone Golem only affects cast spells, not copies of spells put on the stack.

Are any other cards possibly affected by this bug ?
Might also affect other (permanent) cards that copy spells in conjunction with cards that add extra costs to cast spells. I tested Sigil Tracer + Lodestone Golem and it worked as intended (no extra mana payment needed).

Might also affect other cards that add additional costs to cast spells in conjunction with Chandra. the Firebrand. Examples for such cards would be Thalia, Guardian of Thraben, Thorn of Amethyst and Sphere of Resistance.

I confirm this partly as the menu asks you to pay 1 but if you cancel you don't have to pay 1 and the spell is copied correctly.
However I found another bug if you select the ability to copy spell and Chandra, the Firebrand has 2 counters then Chandra, the Firebrand goes to graveyard but doesn't copy the next spell as it should.(probably needs a legacy card to be left for that)?

Fixed the second bug in 278511d
The first one is quite strange, I'll investigate.