AIX 64-bit regex not matching expected

[wkirkboyd]

Compiled TRE on 64-bit AIX using these options:

                    CC='/usr/vac/bin/xlc_r'
                    CFLAGS='-qmaxmem=4096 -qlanglvl=ansi -qarch=pwr5 -qtune=pwr7 -q64'
                    OBJECT_MODE=64
                    export CC CFLAGS OBJECT_MODE
                    BUILD=--build=powerpc-ibm-aix6.1.0.0

./configure --prefix=$DESTINATION --disable-warnings $BUILD

I have a simple string which is expected to match my test expressions in my test.txt file.
Dab

Running these on other platforms produces a match, as well as 32-bit AIX, but not 64-bit AIX.
agrep "^.*(b) test.txt
agrep "^.*.a(b) test.txt

These similar expressions do match my test string.
agrep ".*(b)" test.txt
agrep "^.*.(b)