It looks like the bug still exists in Emacs 26.1 and on latest master.

Attached is an updated patch with change log entries in the commit
message on suggested by
https://www.gnu.org/software/emacs/manual/html_node/emacs/Sending-Patches.html#Sending-Patches.
Please also note that the patch includes a test case update that
verifies that the bug has been fixed.

-- Joel