Embedded tabs always wrap past a certain position

I’m creating documents where there are tabs embedded in the text. It’s fine that I can’t adjust tab stops, etc. but there is a significant problem; when the text reaches a certain width (seems to be about 360 pixels), a tab will wrap the line, regardless of where the right edge of the page is. Doesn’t matter how deeply the item is nested, or what font or size is used, or how many tabs are already in the text, or how wide the page is (as long as there’s room for that 360 pixels): if the current line is past a certain width, then Option-Tab wraps the line.

Here’s a picture of a demo document, with the same text shown with tabs, and then with spaces:

I’ve looked through the style settings, and found nothing apropos. I’ve deleted all the document styles: no change in behavior.

Any idea why this is happening? (It’s been reported before, perhaps not so explicitly, but to no avail…)

I believe there is actually a Ruler in the Format menu that governs the margin widths.