top_sn is used in lots of places to do with skills and their handling.
Yet in tables.c load_socials you will find

void load_socials(  )
{
   FILE *fp;

   if( ( fp = fopen( SOCIAL_FILE, "r" ) ) != NULL )
   {
      top_sn = 0;

Setting it to 0 while loading socials isn't needed and could have bad affects.
Also in tables.c load_commands you will find

void load_commands(  )
{
   FILE *fp;

   if( ( fp = fopen( COMMAND_FILE, "r" ) ) != NULL )
   {
      top_sn = 0;

Again setting it to 0 while loading commands isn't needed and could have bad affects.

Commands and socials are both loaded before the skill table, so this has no affect. It's just an irritation, not a bug. But I'll make the change anyway