[O] Bug : Subscripting not properly working

[Xavier Garrido]

Dear Orgers,

I get a strange behavior when using subscripting /i.e./ =_= char. Here 
is a minimal example

subscripting.org
----------------
#+OPTIONS: ^:{}

The file a_b_c works.

The file a_b_c_d does not work.

The file =a_b_c_d= works again.

When exporting to pdf through LaTeX, the first and last lines export 
properly while the second line gives the following result

The file a_b d__cdoes not work.

The problem occurs when using more than 2 underscores.

Cheers,
Xavier