(In reply to mirh from comment #10)
> Ping (and I wonder if this couldn't be any related to Steam segfaults)

It appears that it is. At least I just tried to run steam on top of a NV34 and
this is the cause of a crash there after logging in. The password screen is
pretty broken already due to steam trying to use NPOT textures, but those
should work OK on nv4x.

Still no clue why it's happening, but at least I can repro myself now, which
means I can investigate properly.