From the Patch 6 notes: Fixed Transmutation Stones not being destroyed when their casters leave the party.
It is completely unjustifiable to me that Larian considers this a fix and the behavior pre patch 6 isn't simply intended. Wizard is already the weakest dedicated caster across the board, and Transmutation is one of its weakest subclasses since its built to be completely passive. Why in the world the Transmutation Stone is supposed to be destroyed when the caster leaves the party is such a weird and unnecessary choice.
There's also no merit in claiming this is TT or RAW justification because BG3 is more homebrewed than mom's chicken soup. Please undo this change and leave Transmuter alone. Wizard's weakest subclass doesn't need a damn nerf!