Opening another window onto the same view/buffer (even at page 1) prevents the flip-flopping.

Weird.

Closing the extra window doesn't re-start flip-flopping unless document-update-all is done.

See the attached document (and stylesheet).

It has professional typesetting algorithm set.

At the bottom of page 26 there is a forward reference to 27a

Look at the top of page 27, the chunk is called 26f but should be 27a.

Click on Tools->Update->Styles

Now the chunk from the top of 27 has moved to the bottom of page 26 and should be called 26f but is now called 27a.

We can talk about the mechanism for a macro working out what page it is on (it inserts a label and then reads the binding to get the page number), but that's not the point; it would work if the paragraph didn't keep switching around.

The label business aside, if the paragraphs keep flipping around then there is a good chance that a new edition of an article or book that fixes a spelling on the last page could have other paragraphs on different pages than the previous revision.

Most interestingly as I try to document this I find that exporting a pdf makes the layout stable for a few iterations (or maybe until I do "document->update-all") at which point it becomes unstable again.

I will try and find a workaround for reseting counters each page, but the issue here is the flip flopping.

I realise that sometimes use of a reference whose label changes size can materially affect the typesetting if the label text size changes as the page number changes, e.g. 99 to 100, but that isn't happening here as far as I can tell.