Which apache2-mpm-* package are you using?
pwb@pwb:~$ dpkg -l apache2-mpm-prefork Desired=Unknown/Install/Remove/Purge/Hold| Status=Not/Inst/Cfg-files/Unpacked/Failed-cfg/Half-inst/trig-aWait/Trig-pend |/ Err?=(none)/Hold/Reinst-required/X=both-problems (Status,Err: uppercase=bad)
||/ Name Version Description +++-=========================-=========================-==================================================================ii apache2-mpm-prefork 2.2.9-1 Traditional model for Apache HTTPD