# "Can't use an undefined value as an ARRAY reference": 
# @{$$n{'x'}} and die;  

print "\n\nnow the same but in loop:\n"; 
for my $e (@{$$n{'x'}}) { 
}
print "why 'x' autovivified?\n"; 
print Dumper $n;
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Well you get right the same effect without disabling autovivification.

While it feels like autovivification there's IMHO technically an aliasing/for-loop magic happening. This is probably not covered by the internal autovivification mechanisms (i.e. explicitely accessing sub-elements) and hence was forgotten.

Not sure if it's easy to implement, but you should commit a bug report to raise the question.