Is there any debug message in the output? Because it calls _wassert and then abort(), as if there was an error condition that Gosu/libogg is checking for.
How did you generate the ogg files? You could try exporting them again from Audacity (aah quality loss!!), at least for now. Maybe some bizarro tool uses the index. (Speculation: They might use the additional streams to implement segments for looping?)
Yeah, because Release builds don't have assert() in them. If the sample/song sounds correct as well, maybe I should just remove this assert()... I was being a bit defensive there because I have no clue what this stream thing even means. :)