automake's Per-Object Flags Emulation --- CFLAGS override or just prepend ?

[Michele Martone]

Hi,

I'm using the "Per-Object Flags Emulation" functionality of automake
to build a single library (.a) file from two .a files, each made of .o
files compiled with different flags.

In order to apply the example of
 http://www.gnu.org/software/automake/manual/automake.html#Per_002dObject-Flags 
in my Makefile.am, I declare something similar to
  libfoo_a_CFLAGS = -some -other -flags
expecting that libfoo.a will be compiled with -some -other -flags 
rather than CFLAGS.

However in the resulting Makefile I see that something like the
following:
 libfoo_a-foo.o: foo.c
         $(CC) ... $(libfoo_a_CFLAGS) $(CFLAGS) ...
is being generated instead.
In other words, CFLAGS is not being replaced by libfoo_a_CFLAGS: only
prepended: this does not seem neither what the documentation says nor
what I need.

Am I doing something wrong ?