I assume that there is something wrong with the texture id’s, it randomly draws incorrect(other) textures that also use surface.SetTexture.
This is a general annoyance I noticed while fixing up PlayX(and dozens of times before), this bug also appeared in gmod13 and is the reason no one should ever use surface.SetText.
[editline]8th July 2012[/editline]
After further investigation it looks like that it’s NOT the same problem as the surface.SetTexture bug, since the sound isn’t work in these situations either.
Having the surface.SetTexture bug fixed would be neat though.