superfluous test in AC_CHECK_HEADERS?

Hi,

I'm using 

AC_CHECK_HEADERS([ecl.h])

in configure.ac, and that gives the following in the log file
(autoconf 2.57):

configure:5067: checking ecl.h usability
configure:5080: gcc -c -g -O2  -I/proj/contrib/lkb/latest/include 
-I/proj/contrib/lib/ecl/h conftest.c >&5
configure:5083: $? = 0
configure:5086: test -s conftest.o
configure:5089: $? = 0
configure:5099: result: yes
configure:5103: checking ecl.h presence
configure:5114: gcc -E  -I/proj/contrib/lkb/latest/include 
-I/proj/contrib/lib/ecl/h conftest.c
configure:5120: $? = 0
configure:5139: result: yes
configure:5175: checking for ecl.h
configure:5182: result: yes

It first tests whether it can compile with the header file, and
then tests if the file exists or not.  Is the second test not
subsumed by the first one (if that one is successful)?

Thanks,

Frederik Fouvry