Had I tested my assumption, I would have come to that same conclusion:

perl -we "print -d SCRIPTS"
Name "main::SCRIPTS" used only once: possible typo at -e line 1.
-d on unopened filehandle SCRIPTS at -e line 1.
Use of uninitialized value in print at -e line 1.
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I thought the bareword would be treated as a string, but it gets treated as a filehandle.

That's what I get for not using the old ways but lexical filehandles wherever I can :).