Recursion error from launching a demo file in etsdemo with Wx

Launching the etsdemo application with WxPython has quite a few problems, mostly to do with traitsui rather than the application itself, but here is one that seems specific to the demo application:
If there are any example files in the application, clicking a Python file (i.e. demo code) will throw this (recursion) error:

```
Fatal Python error: Cannot recover from stack overflow.
Python runtime state: initialized

Thread 0x000070000d34e000 (most recent call first):
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/pyface/image/image.py", line 282 in _process
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/threading.py", line 870 in run
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/threading.py", line 932 in _bootstrap_inner
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/threading.py", line 890 in _bootstrap

Current thread 0x00000001128addc0 (most recent call first):
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/threading.py", line 1314 in current_thread
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/traits/trait_notifiers.py", line 615 in dispatch
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/traits/trait_notifiers.py", line 522 in _dispatch_change_event
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/traits/trait_notifiers.py", line 549 in _notify_method_listener
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/traits/trait_notifiers.py", line 476 in __call__
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/etsdemo/app.py", line 229 in write
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/traitsui/wx/code_editor.py", line 333 in _style_document
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/traitsui/wx/code_editor.py", line 249 in update_editor
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/traitsui/editor.py", line 524 in _update_editor
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/traits/trait_notifiers.py", line 616 in dispatch
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/traits/trait_notifiers.py", line 522 in _dispatch_change_event
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/traits/trait_notifiers.py", line 549 in _notify_method_listener
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/traits/trait_notifiers.py", line 476 in __call__
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/etsdemo/app.py", line 229 in write
...
(more of the same)
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/traitsui/wx/code_editor.py", line 333 in _style_document
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/traitsui/wx/code_editor.py", line 249 in update_editor
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/traitsui/editor.py", line 524 in _update_editor
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/traits/trait_notifiers.py", line 616 in dispatch
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/traits/trait_notifiers.py", line 522 in _dispatch_change_event
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/traits/trait_notifiers.py", line 549 in _notify_method_listener
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/traits/trait_notifiers.py", line 476 in __call__
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/etsdemo/app.py", line 229 in write
File "/Users/kchoi/Work/ETS/venvs/etsdemo-test/lib/python3.8/site-packages/traitsui/wx/code_editor.py", line 333 in _style_document
...
Abort trap: 6
```