A little faffing and I worked out that WINEDEBUG=+ddraw would tell me what textures were allocated and released and supplied to various calls. And in this case, the texture was allocated, and released, and *then* passed to a SetTexture call! Which didn't work, because... it was no longer a texture. Then it took a lot a lot more faffing to find where and why these things happened. Ended up having to compile wine to insert debug prints because winedbg and gdb both just crashed -_-