IDLE edit windows ignores tab settings

[Lith]

[Python/IDLE newbie here]

I created a .py file in UltraEdit and saved it. I use (and always will,
despite the FAQ's recommendation against it) tabs instead of spaces,
set to 4 spaces per tab.

When I open the file in IDLE, suddenly the tabs are 8 spaces wide. This
is despite the fact that I've gone to
Options menu > Configure IDLE... > Fonts/Tabs
and set it thusly:
    Tab key inserts tabs
    indent width 4

Is this a bug, or am I missing something?

I'll now go google to see who to blame for the original 8-space tab.