library versioning problem

[Lucien GENTIS]

Hi to all,

I would like to use libtool to manage versioning of a library called, 
say "mylib"
libtool version is 1.5.6-6 under Linux Debian Sarge 3.1 stable

In the configure.ac at the project root, I have the lines:
mylib_CUR=69
mylib_REV=47
mylib_AGE=38
AC_SUBST(mylib_CUR)
AC_SUBST(mylib_REV)
AC_SUBST(mylib_AGE)

In project sources dir, Makefile.am contains:
mylib_la_CPPFLAGS="-Dmylib_CUR=${mylib_CUR}" "-Dmylib_REV=${mylib_REV}" 
"-Dmylib_AGE=${mylib_AGE}"
mylib_la_LDFLAGS=-version-info ${mylib_CUR}:${mylib_REV}:${mylib_AGE}

I configure the library with:
./configure --prefix=/usr/local/mylib-69.47.38-i18n

So I expected to find mylib.so.69.47.38 in 
/usr/local/mylib-69.47.38-i18n/lib, but instead of that, I find 
mylib.so.31.38.47

That means:
CURRENT is replaced by CURRENT - AGE      (69 - 38 = 31)
REVISION is replaced by AGE
AGE is replaced by REVISION

Surely, I misunderstood something, so an explanation would be very nice

Thanks in advance

Lucien