[KevinH]

Okay, I finally got my Manjaro Linux box updated and working again. Built Sigil and installed it. Then ran your test case and had no "extra" pages at the end of any chapter.

So whatever is happening is specific to your Linux setup as both Arch and Manjaro seem to handle it all properly with the latest Bibi plugin. I also tried various screen and font sizes using Bibi preferences and it all just worked.

So perhaps the issue is missing or damaged fonts with bad font metrics. Not sure here.

And for the record here is what DiapDealers bash script says about my fonts:

serif: NotoSerif-Regular.ttf: "Noto Serif" "Regular"
sans-serif: NotoSans-Regular.ttf: "Noto Sans" "Regular"
monospace: NotoSansMono-Regular.ttf: "Noto Sans Mono" "Regular"
Arial: LiberationSans-Regular.ttf: "Liberation Sans" "Regular"
Helvetica: NimbusSans-Regular.otf: "Nimbus Sans" "Regular"
Verdana: NotoSans-Regular.ttf: "Noto Sans" "Regular"
Times New Roman: LiberationSerif-Regular.ttf: "Liberation Serif" "Regular"
Courier New: LiberationMono-Regular.ttf: "Liberation Mono" "Regular"

which matches his I think.