php as shipped uses libgdbm for db-files. when you remove gdbm from your system and rebuild, it uses the libdb that is part of the glibc-package, which is the appropriate lib for sharing dbmfiles with perl and sendmail. Simply adding --without-gdbm doesn't work (bug in php configure?) Is there something like build-conflicts in specfiles?
I overlooked the dba_* functions. just forget it. Although it would be nice to have ndbm the default for dbm or mark dbm_* as deprecated.