Disabled safe mode when using PHP 4.2, re-enabled safe mode just recently using 4.2.2.  Running a script that includes another script that does not have a matching UID generates the appropriate error message but restarting Apache afterwards generates:

Starting httpd: Ouch! ap_mm_create(1048576, "/var/run/httpd.mm.2126") failed
Error: MM: mm:core: failed to acquire semaphore (No space left on device): OS: Identifier removed

Disabling safe mode has had no effect when only Apache was restarted.  Restarting the system with safe mode disabled returns things to normal.  Re-enabling safe mode, restarting Apache and running any script causes the error to return.

Fairly generic Red Hat 7.2 system with KDE 2.2.2. 

./configure --prefix=/usr \
--exec-prefix=/usr \
--bindir=/usr/bin \
--includedir=/usr/include \
--infodir=/usr/share/info \
--libdir=/usr/lib \
--libexecdir=/usr/libexec \
--localstatedir=/var \
--mandir=/usr/share/man \
--sbindir=/usr/sbin \
--sharedstatedir=/usr/com \
--sysconfdir=/etc \
--datadir=/usr/share \
--enable-bcmath \
--enable-calendar \
--enable-dbx \
--enable-exif \
--enable-ftp \
--enable-gd-native-ttf \
--enable-magic-quotes \
--enable-mbstring \
--enable-memory-limit \
--enable-safe-mode \
--enable-shmop \
--enable-sockets \
--enable-sysvsem \
--enable-sysvshm \
--enable-track-vars \
--enable-trans-sid \
--enable-wddx \
--with-apxs=/usr/sbin/apxs \
--with-bz2 \
--with-config-file-path=/etc \
--with-curl \
--with-db3 \
--with-dom \
--with-expat-dir=/usr \
--with-freetype-dir=/usr \
--with-gdbm \
--with-gd=/usr \
--with-gettext \
--with-gmp \
--with-gnu-ld \
--with-imap-ssl=/usr \
--with-imap=/usr \
--with-jpeg-dir=/usr \
--with-kerberos=/usr/kerberos \
--with-layout=GNU \
--with-ldap=/usr \
--with-mm=/usr \
--with-mysql=/usr \
--with-ncurses \
--with-openssl=/usr \
--with-png-dir=/usr \
--with-pspell=/usr \
--with-qtdom \
--with-regex=system \
--with-unixODBC=/usr \
--with-zlib=/usr