Skeletal Warrior Minions' spirit cost changes when they respawn

When I equip the "Rattling Sceptre", it gives me 2x Skeletal Warrior for 0 spirit automatically. However when I have them with other minions somehow when they die and revive the first two free ones become regular spirit cost ones ?

Below I have 7 minions, but when those warriors die and revive game counts them as if they have spirit cost and removes one of the Sniper/Mage. So, I start with 7 minions, few packs later I have 6 minions with exact same spirit reservation.

I can fix that only if I remove all the Warriors and start summon them again from the skill interface. Once the 7 minions became 6, they don't go back to 7 because I don't have enough spirit.

For context; I have 230 spirit.
40 spirit for Withering Presence + Clarity I
74 spirit for 2x Skeletal Sniper (lvl 6) + Last Gasp
49 spirit for 1x Skeletal Frost mage (lvl 5)
50 spirit for 4x Skeletal Warrior (lvl 6) + Last Gasp
and 17 remaining spirit.

It's not like game removes the Mage and summons 2 more warriors with 66 (49+17) spirit.