https://bugs.winehq.org/show_bug.cgi?id=38274
--- Comment #35 from Sergey Isakov isakov-sl@bk.ru --- Thanks for confirming the bug.
I can say that the bug presents with all HeroesVI versions and with all Wine versions including wine-stage. Replacing libraries d3dx*** to native doesn't help. The bug present. The bug is not related to DXTn support. I made it and the bug is still here. The bug seems to be in wined3d.dll interpreting volume textures. I saw that the game assumed XZ slice (up view) while wined3d uses XY slice (front view). May be this is the root.
The bug is absent in real Windows 7.