There are two possible workarounds:
a: Change any setting in the Hosting Settings, save it and turn it back. I did it with a switch from P>HP as Apache Module to FastCGI and back.
b: As RedEnzian wrote above: run /usr/local/psa/admin/bin/httpdmng --reconfigure-all on your machine. It should work, too
Addendum: Workaround b does not solve the problem. You have to to do Workaround a for every Domain and subdomain with a website.
@Parallels: please try to find a solution, as it is not really amusing, to manually correct that issue. And, as you may have noticed, I am not the only customer suffering from that Problem.