Missing last element in backtrace

[asfluido]

Hello world. If I execute this little test script:

class C
  def runme    
    raise 'a'
  end
end

C::new.runme

I obtain the expected output:

trace:
	[0] /tmp/test1.rb:3:in C.runme
	[1] /tmp/test1.rb:7
/tmp/test1.rb:3:a (RuntimeError)

If my script is, instead, this one:

class C
  def runme    
    a=1*nonexisting
  end
end

C::new.runme

(that is, if I try to make use of a non-existing variable), this is the result:

trace:
	[0] /tmp/test2.rb:7
/tmp/test2.rb:7:undefined method 'nonexisting' for #<C:0x2376170> (NoMethodError)

As you can see, the most recent line of the backtrace is missing. I got it back by commenting the following three lines from backtrace.c (currently at L.275):

  else if (mrb->backtrace.n > 0) {
    print_backtrace_saved(mrb);
  }

I now receive:

trace:
	[1] /tmp/test2.rb:3:in C.runme
	[0] /tmp/test2.rb:7
/tmp/test2.rb:7:undefined method 'nonexisting' for #<C:0x1438170> (NoMethodError)

but this is most probably not the proper fix: I have recovered the missing backtrace element, but the error message still points to the wrong script line (7 instead of 3).

Ideas?