It is not an inconsistency

only lvalues get autovivified, and undef is not an lvalue

$ perl -le " sub dang : lvalue { undef } dang()=1;  "
Can't return undef from lvalue subroutine at -e line 1.

$ perl -le " sub dang : lvalue { undef } dang()->[0] "
Can't use an undefined value as an ARRAY reference at -e line 1.

$ perl -le " undef->[0] "
Can't use an undefined value as an ARRAY reference at -e line 1.

$ perl -le " my $variable = undef; $variable->[0] "
[download]

Even though undef can resemble an lvalue (hey, its on the left of an assignment),

( undef, undef, my $mode ) = stat 'filename';
[download]

you can't assing a value to undef, so undef is not an lvalue

$ perl -le " undef = 1; "
Modification of a read-only value attempted at -e line 1.
[download]

See References quick reference, autovivification, perlglossary#autovivification, autovivification, lvalue