Bug found!
I were stupid not seeing it before. After some further tests i finally found the problem:
It all depends on your research!
If your nation researched 'Call of the Wild' (Conjuration 3) the Soulstone of the Wolves works perfect.
If your nation researched 'Astral Travel' (Thaumaturgy 9) the Gates Stone works perfect.
If not: It will not work!
I'm not sure there are other items with the same problem, maybe some further tests are needed.
However this should be in the bug list, i don't think its WAD that you've to research the spell before using it with an item.
Re: Gate Stone
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