Hi,

I noticed something unexpected in org-beamer.el when I used overlay 
specifications together with optional parameters for the frame 
environment and the frame contained verbatim sections. In this case the 
exporter would add [fragile] to the frame options in a way that would 
break the LaTeX code.

I wrote a small patch that fixes this particular problem for me.

The following test case generates invalid LaTeX code with org-mode 
revision c4b23345. With the attached patch it generates valid LaTeX code.

#+LaTeX_CLASS: beamer
* overlay + optional parameter
   :PROPERTIES:
   :BEAMER_envargs: [label=abc]<1>
   :END:
   #+BEGIN_LaTeX
   \begin{verbatim}
     I am [fragile]
   \end{verbatim}
   #+END_LaTeX

Christoph