You explained it very well and I can duplicate your problem and then suddenly it stopped showing the problem and all was OK.
The only thing I can suggest is click in one of the fields for something else, apply a number,. and then try space after.
This problem is asked and answered already many, many times over here before: change the text preferences to NOT show the OpenType adornment on selection and text frames.
You're right, I should have searched more thoroughly in the forum first. I appreciate it, that worked!
Ahhh, now I got it!
One more thing, though. If you click, not select, the text, the problem doesn't happen. Mostly because there is no OpenType adornment visible when you click.
It's OK for setting paragraph attributes for a sing paragraph, but not if you need to work on several paragraphs.