Help - starting to use ditaa/artist-mode in org-mode and mode wrong some of the time

[unfrostedpoptart]

I'm trying to use ditaa in babel source blocks in an org-mode document.  I'm 
seeing a strange behavior.  Some of the time I use c-c ' (org-edit-special) to 
open the diagram in a new buffer for editing, it comes up correctly in 
artist-mode.  However, many times, the buffer is just in text mode.

What am I missing?

Thanks,

 David