Could you try the following:
Type in a bash command line:
export LANG=en_US
And then recompile in that same shell ?
(do a './build clean' first, then a './build update', put the changes in the config.php again for imap, then a './build php', might even want to remove the php-4.3.4 source directory)
There's a bug in the plain RH9 release of bash, which has a weird language setting, and it messes up a certain range of compiles (Perl's CPAN completely breaks if you try to compile something in a plain RH9 setup without updates)
Dunno if this causes it, but it's worth a shot..