perldoc -f do
"do BLOCK" does *not* count as a loop, so the loop control
statements "next", "last", or "redo" cannot be used to leave or
restart the block. See perlsyn for alternative strategies.
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If you've got a loop in which you're calling nextline, your loop is going to restart every time sub hits that next. This code:

for (10..13) {
  print "Top loop $_\n";
  do_sub($_);
  print "-- after sub\n";
}

sub do_sub {
  my ($a) = shift;
  do {
    next if $a < 15;
    print "Sub $a\n";
  } while ($a < 20);
}
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yields this output (notice neither the print in the sub nor the print 'after sub' lines ever execute):

Top loop 10
Exiting subroutine via next at try2.pl line 14.
Top loop 11
Exiting subroutine via next at try2.pl line 14.
Top loop 12
Exiting subroutine via next at try2.pl line 14.
Top loop 13
Exiting subroutine via next at try2.pl line 14.
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