I’ve found the problem, and it’s a stark reminder of why detail matters.
I have a second view component which renders another form. The problem being, it tries to render a form within a form (which is invalid HTML for a start). if I remove this, all areas of the form work and submit as expected. I wasn’t seeing this, as the resulting markup didn’t include the second form in full, although does add the ufprt field. I figure Umbraco was falling over with confusion here,
I was trying to keep code sample as simple as possible, had I been a touch more detailed someone with fresh eyes would’ve spotted this right away.
A touch embarrassing to say the least. This is not an Umbraco problem, but a me problem, well I’ll blame the original developer!
Thanks for your help.