TYPO3 Core

I recently switched to PHP 5.2 and I can't edit placed plugins anymore.
The edit form doesn't load. The page is blank, and when I display the source, there's a login timeout message.
Standard content can be edited normally, without error.

Here's my PHP 5.2 configuration commande. Note that it's exactly the same as the configuration of working PHP 5.1.4:

./configure --prefix=/usr/local/php5-apxs2 --with-config-file-path=/usr/local/php5-apxs2 --with-apxs2=/usr/local/apache2/bin/apxs --with-kerberos=/usr --with-ldap=/usr/local/openldap --with-mysql=/usr/local/mysql --with-mysql-sock=/tmp --with-mysqli=/usr/local/mysql/bin/mysql_config --with-pdo-mysql=shared,/usr/local/mysql --with-iodbc=/usr --enable-dbx --with-zlib-dir=/usr --with-bz2 --enable-sysvsem --enable-sysvshm --enable-sysvmsg --enable-shmop --enable-sockets --enable-trans-sid --enable-mbstring --with-gettext=/usr/local --enable-exif --with-tiff-dir=/usr/local --with-jpeg-dir=/usr/local --with-png-dir=/usr/local --with-freetype-dir=/usr/local --with-gd --enable-gd-native-ttf --enable-gd-imgstrttf --with-curl=/usr --enable-ftp --enable-filepro --disable-rpath --with-xml --with-soap --enable-soap --enable-bcmath --enable-calendar --enable-cli --disable-debug
(issue imported from #M4507)