ProcBackground::Init() is not mentioned on the Proc::Background CPAN page, hence I have not used it. I have been using the OO interface as documented in the POD.
And again, the documentation on that CPAN page is about using Proc::Background to start outside processes, not to start pieces of your program in a new process. It is not a drop-in fork replacement, nor do the docs imply this to me.
METHODS new [options] command, [arg, [arg, ...]] new [options] 'command [arg [arg ...]]'
All of these functions take commands as arguments, as they would be invoked by system(""). Perhaps you are using an internal API you are not meant to use? It is not documented!