Using AddSoulgem fills all soul gems of the specified type
Using the AddSoulGem script function seems to add an additional soulgem and fills it with the correct soul; however, it also adds that soul to any other empty soul gems of that type.
@Player->AddSoulGem "nix-hound", Misc_SoulGem_Petty@
If the player has 4 empty Petty Soul Gems, the result will be a stack of 5 petty soul gems, all of which are filled with Nix-Hound souls.
This issue occurs in OpenMW 0.43.0. From my testing, it seems to occur every time. I have not tested it while having filled soul gems of the same type in the inventory.
(RM-4351 from redmine: created on 2018-03-09 by Nick S, , closed on 2018-03-10 by Andrei Kortunov)