ModPlug Tracker (and maybe some others but that's rather unlikely) used 7-bit panning with surround command 8A4 for MOD files, much like the X command in the S3M format. However, it was much more common to have 8-bit panning (without surround) in MOD files, like FT2 did it, so OpenMPT uses 8-bit panning these days.
If OpenMPT detects that a MOD file uses 7-bit panning, it will convert it to 8-bit panning on import and converts command 8A4 to its IT/S3M equivalent S91 (but since that command does not exist in MOD files it is shown as a questionmark).
Most players will most likely assume 8-bit panning and not do the same conversion from 7-bit panning as OpenMPT does, so it's not a good idea to rely on this hack.
