I have been looking at this pretty hard, but I can't find any reason why it's bugging out, at least not with the OGG system. I may have overlooked something but basically, the function that is bugging out is a long way down the call-chain and is not directly used by the OGG system. In addition, the crash occured when there were no OGG files available, which causes the OGG system to shut itself down immediately. As I am unable to replicate the crash, please try playing with the cvar "ogg_enable" set to 0. If the crash persists, the problem is somewhere else, or I've missed something (more likely). The other sound addition of build 26 was the first set of surface specific sounds - this code does not directly call the bugged function either - it is only called by other untouched sound functions, indicating that there may be some specific sound data that the function does not agree with. I'm going to try reproducing the bug again when I have some time, hopefully getting gdb to output some more useful information.
edit: If it only happens in-game, can you check if those maps you are getting crashes on use snow textures or w_metal1 (you can just search the bsp file for them)?
edit2: Not sure if S_IssuePlaySound is even used by ogg indirectly, as part of the stuff it does is dealing with attenuation and spatialisation.
