[OS X Emacs] Save buffer untabifies in Aquamacs?

[C. R. Oldham]

Greetings,

I've been an Emacs user for 20+ years and finally can move to the Mac  
platform fulltime.  I've noticed that Aquamacs seems to untabify  
buffers by default on save, so for example when I use Aquamacs to  
manipulate tab-separated data files on save all my tabs disappear.   
Can someone please tell me where to turn that behavior off?  Thanks.

--cro