IndexError: string index out of range

[themusicgod1]

After hitting what I thought at least was one of the numbered buttons(I think it was a 2 but am not 100% sure) ...an error message came up:

Traceback (innermost last):
  File "/usr/lib/python3/dist-packages/mnemosyne/pyqt_ui/review_wdgt.py", line 396, in grade_answer
    self.review_controller().grade_answer(grade)
  File "/usr/lib/python3/dist-packages/mnemosyne/libmnemosyne/review_controllers/SM2_controller.py", line 153, in grade_answer
    self.show_new_question()
  File "/usr/lib/python3/dist-packages/mnemosyne/libmnemosyne/review_controllers/SM2_controller.py", line 123, in show_new_question
    self.update_dialog()
  File "/usr/lib/python3/dist-packages/mnemosyne/libmnemosyne/review_controllers/SM2_controller.py", line 200, in update_dialog
    self.update_qa_area(redraw_all)
  File "/usr/lib/python3/dist-packages/mnemosyne/libmnemosyne/review_controllers/SM2_controller.py", line 233, in update_qa_area
    self.render_chain, no_side_effects=True))
  File "/usr/lib/python3/dist-packages/mnemosyne/libmnemosyne/card.py", line 96, in answer
    (self, render_chain, **render_args)
  File "/usr/lib/python3/dist-packages/mnemosyne/libmnemosyne/card_type.py", line 75, in render_answer
    render_answer(card, **render_args)
  File "/usr/lib/python3/dist-packages/mnemosyne/libmnemosyne/render_chain.py", line 142, in render_answer
    return self._render(card, fact_keys, decorators, **render_args)
  File "/usr/lib/python3/dist-packages/mnemosyne/libmnemosyne/render_chain.py", line 153, in _render
    card, fact_key, **render_args)
  File "/usr/lib/python3/dist-packages/mnemosyne/libmnemosyne/filters/RTL_handler.py", line 49, in run
    if text[0] in string.ascii_letters or text[1] in string.ascii_letters:
 IndexError: string index out of range

Ubuntu: artful 17.10
mnemosyne: 2.4-0.1

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: mnemosyne 2.4-0.1
ProcVersionSignature: Ubuntu 4.13.0-25.29-generic 4.13.13
Uname: Linux 4.13.0-25-generic x86_64
ApportVersion: 2.20.7-0ubuntu3.7
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Sun Jan 28 17:25:46 2018
InstallationDate: Installed on 2017-04-18 (285 days ago)
InstallationMedia: Ubuntu 17.04 "Zesty Zapus" - Release amd64 (20170412)
JournalErrors:
 Error: command ['journalctl', '-b', '--priority=warning', '--lines=1000'] failed with exit code 1: Hint: You are currently not seeing messages from other users and the system.
       Users in the 'systemd-journal' group can see all messages. Pass -q to
       turn off this notice.
 No journal files were opened due to insufficient permissions.
PackageArchitecture: all
SourcePackage: mnemosyne
UpgradeStatus: Upgraded to artful on 2017-10-19 (101 days ago)

[Peter Bienstman (peter-bienstman)]

BTW, this has long been fixed upstream in Mnemosyne, which is now at version 2.6.