Thank you very much for your advice.

I have tried Jon Orwants example (persistent.pl/persistent.c) in perlembed with the sameesults.

So, I have tried out perlbug.

Thanks again for you advice; unfortunately this work is a small part of the Netsaint/Nagios (http://www.Netsaint.ORG) project, so development versions of Perl are not an option.