Have you tried installing apache with a different MPM module? If your website/webapp uses a connector to a multithreaded backend (ajp13?), you might want to try using the worker MPM.
#apt-get install apache2 apache2-doc apache2-mpm-worker apache2-utils libexpat1 ssl-cert
The error message itself might be a bug:
The work around is to do a hard restart instead of a graceful restart when using mod_prefork.
If you have apache managing multiple ajp13 backend connections, I would try running mod_worker, not as a workaround to this bug, but for better performance and reliability.