mod_folder upgrade fails to due duplicate SHA1 hashes

My Moodle 1.9 installation contains files

48/resource/guide/lesson01.html
10/resource/guide/lesson01.html

When I attempt an upgrade, both files result in the same field values in $newrecord in create_file_fromstoredfile (file_storage.php) and so $DB->insert_record fails.

I attempted an upgrade from 1.9.11 to 2.1.1, with no special steps taken. All prerequisites were met and so on - it just fails to do the upgrade, due to the issue described above. I can reliably reproduce the issue by scrubbing the database and Moodle data folder and recopying them from the 1.9 installation (I'm working on a copy).

Others apparently have the same issue (see the URL provided below).

I am a software developer, with Eclipse installed locally; I'm willing and able to test patches.