I am unable to confirm that the module plays restarts from the last pattern. However, the module doesn't reset its tempo to the default anyway when looping, so there's not much of a point in looping it. Not all modules are made to loop properly, and this module would not loop properly in ScreamTracker 3 either.

The point is the song doesn't end when the pattern loop is over, libopenmpt doesn't return 0 samples but continue to play for 13 minutes.

I see now some things in S3M-specific pattern loop handling a broken. Investigating...

Fixed in r18176 (trunk) and r18177 (OpenMPT 1.30 / libopenmpt 0.6).