1. This is first a reproducable functional bug due to the interaction between the section and footnote logic.
When creating a "Same Page" section break, it can happen that a footnote must be displayed on the same page, but the section at the end of the page does not correspond to the section where the footnote was added.
Presently, NWP can't handle this and generates a page break so that the footnote is appearing with the initial section. This is reproducable. (see attached file)
2. My gut feeling about the crash:
When creating a footnote in a same page section, the system enters an unstable state. When you start teasing the system playing with the section properties (e.g. changing "start on" property, the system crashes, as far as I see, erratically.
For large documents, sections are important; a fix even in beta (using NWP 3.4.1. beta 1) would be nice. It's a bit of a showstopper for me

Cheers