Whenever I put an empty headline and I add some tag like :B_note: or
whatever, the tag end up in the headline.

** Some Frame
***                                                                :B_note:
:PROPERTIES:
:BEAMER_env: note
:END:
[2012-09-03 lun. 09:22]
blah blah

is exported as :

\begin{frame}{Some Frame}
\note{:B\_note:
blah blah}
\end{frame}

I think that the tag should never be used for the headline.
What about you ?

-- 
Fabrice