Cannot edebug in tabbar.el.

[BobD]

Using emacs GNU Emacs 24.5.1 (i686-pc-mingw32) of 2015-04-11 on LEG570
tabbar.el:
  ;; Revision: $Id: tabbar.el,v 1.7 2009/03/02 21:02:34 davidswelt Exp $
  tabbar-version "2.0"

I ran edebug-defun in several tabbar functions, e.g. (tabbar-buffer-groups).
No breaks when function entered.
I added (message "Entered tabbar-buffer-groups") to (tabbar-buffer-groups).
The message appears dozens of times.

I tried this with "-*-no-byte-compile: t; -*-" present and absent.  No 
difference.

I was able to get a couple of functions to break into the debugger.

Any thoughts on how tabbar.el is selectively blocking edebug?