I'm confused, for me it looks like you are just assigning the old values back.²

And if IIRC nested packages are hold in the %main:: stash.¹

So either your example is wrong or I'm lacking enough understanding of whats going on.

1) wrong, I misunderstood perlmod

{
  package ding::dong;
  $x=1
}
 
$\="\n";
 
print $ding::dong::x;                       # prints 1
 
print $main::{"ding::"};                    # *main::ding::
 
print $main::{"ding::"}->{"dong::"};        # *ding::dong::
 
print $main::{"ding::"}->{"dong::"}->{x};   # *ding::dong::x
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2) AHH now I got it... you're just keeping the sub packages (here "dong::" of "ding::") and cleaning anything else.