Confusing behavior by Ruby Debugger using 'n' (or next) command.

gistfile1.txt

[5] pry(main)> prime? 5
[2, 11] in /Users/kdavh/Google Drive/cs/2013 App Academy/Coursework/w1d1/primes.rb
   2  require 'debugger'
   3
   4  def prime?(num)
   5    debugger
   6
=> 7    (2..num/2).each do |i|
   8      if (num % i) == 0
   9        return false
   10      end
   11    end
/Users/kdavh/Google Drive/cs/2013 App Academy/Coursework/w1d1/primes.rb:7
(2..num/2).each do |i|
(rdb:1) n
[3, 12] in /Users/kdavh/Google Drive/cs/2013 App Academy/Coursework/w1d1/primes.rb
   3
   4  def prime?(num)
   5    debugger
   6
   7    (2..num/2).each do |i|
=> 8      if (num % i) == 0
   9        return false
   10      end
   11    end
   12    true
/Users/kdavh/Google Drive/cs/2013 App Academy/Coursework/w1d1/primes.rb:8
if (num % i) == 0
(rdb:1) n
[7, 16] in /Users/kdavh/Google Drive/cs/2013 App Academy/Coursework/w1d1/primes.rb
   7    (2..num/2).each do |i|
   8      if (num % i) == 0
   9        return false
   10      end
   11    end
=> 12    true
   13  end
   14
   15  def primes(num_primes)
   16    debugger
/Users/kdavh/Google Drive/cs/2013 App Academy/Coursework/w1d1/primes.rb:12
true
(rdb:1) n
[324, 333] in /usr/local/rvm/gems/ruby-1.9.3-p194@global/gems/pry-0.9.12/lib/pry/pry_instance.rb
   324      target = Pry.binding_for(target)
   325      inject_sticky_locals(target)
   326      exec_hook :before_eval, code, self
   327
   328      result = target.eval(code, Pry.eval_path, Pry.current_line)
=> 329      set_last_result(result, target, code)
   330    ensure
   331      update_input_history(code)
   332      exec_hook :after_eval, result, self
   333    end
/usr/local/rvm/gems/ruby-1.9.3-p194@global/gems/pry-0.9.12/lib/pry/pry_instance.rb:329
set_last_result(result, target, code)
(rdb:1) n
[326, 335] in /usr/local/rvm/gems/ruby-1.9.3-p194@global/gems/pry-0.9.12/lib/pry/pry_instance.rb
   326      exec_hook :before_eval, code, self
   327
   328      result = target.eval(code, Pry.eval_path, Pry.current_line)
   329      set_last_result(result, target, code)
   330    ensure
=> 331      update_input_history(code)
   332      exec_hook :after_eval, result, self
   333    end
   334
   335    # Output the result or pass to an exception handler (if result is an exception).
/usr/local/rvm/gems/ruby-1.9.3-p194@global/gems/pry-0.9.12/lib/pry/pry_instance.rb:331
update_input_history(code)
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