This is file vavoom-1.33/actionhexen/base.txt:

// Default game detection configuration file
//NOTE Games are detected in backwards order

// Default case when IWAD is already set up
game basev/hexen
end

// Hexen
game actionhexen
iwad hex

You need to make your MOD point the game to "basev/hexen", since it's where the main progs will be used from.

I suppose this one has been fixed since the report was made <!-- s:) --><img src="{SMILIES_PATH}/icon_smile.gif" alt=":)" title="Smile" /><!-- s:) -->.