Easy enough to prove it works:

>perl -wMstrict -le
"my $bl_id;
 my @bly_id;
 sub insert_budget_line { return 'foo'; }
 sub insert_budget_line_year { return @_[1,0]; }
 eval {
   $bl_id = insert_budget_line();
   @bly_id = insert_budget_line_year(bl_id => $bl_id);
   };
 print qq{@bly_id};
"
foo bl_id
[download]

How is your  insert_budget_line_year function defined?