This issue was solved with changeset r43634.
Charles, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.
parse.y: remove "f" suffix [ruby-core:57966] [Feature #9042]
revert r42847 "test_string.rb: add test string encoding"
revert r42846 "parse.y: freeze in advance to reduce objects"
revert r42843 "parse.y: deduplicate frozen string literals"
revert r42780 "test_string.rb: yet another test"
revert r42779 "parse.y: valid suffix word only"
revert r42778 "test_string.rb: remove duplicated code"
revert r42775 "parse.y: force_encoding"
This reverts commit 93ea04ecec7639ca8d0e58948e78461434782ecc.
revert r42773 "Add frozen string literals"