Example: Jazz Jackrabbit Bonus stage s3m.
Here how it sounds in the program: http://www104.zippyshare.com/v/Wq2vcuHP/file.html (notice the weird high pitch near the end of the sample)
And here how it sound in the game (how it is supposed to sound like): http://www104.zippyshare.com/v/EAD1nl4V/file.html
There are many bad S3M conversions of old Epic MegaGames soundtracks out there. If you actually play the original PSM files from the game in OpenMPT, you will get the correct playback.