When playing songs that have restart points other than the first pattern in the order list (eg: ALLOYRUN.RAD[2], DRMTST.A2M[3]), AdPlug player loops the song to the beginning of the first pattern in the order list after reaching end of song. By comparison, when playing the song in AdLib Tracker II[1], the song loops back to different places:
File AdPlug Adlib Tracker II
ALLOYRUN.RAD beginning of order 0 beginning of order 04
DRMTST.A2M beginning of order 0 beginning of order 01
To fix this bug, AdPlug plugin needs to support loopback to locations other than beginning of song. While it can be done at library level, the ability to expose this feature to WinAmp-compliant player and integrate it to the player's user interface is uncertain. Maybe it need a XMPlay-style plugin? After all, XMPlay's built-in module player can play modules that loop back to other locations.
[1] http://www.adlibtracker.net/files/at2g3r38.zip
[2] File [1], directory MODULES\VOID\
[3] File [1], directroy MODULES\BRENDAN\
AdPlug does support internal looping, so you could tweak the RAD and A2M players so that they loop back to the repeat point instead of the beginning of the song. I agree it would be better to make the loop information available to the plugin/player, but unfortunately this would require some major changes to the library.