Problem with receipt photos

Has anyone had an issue with iOS 11.4.1 where ‘adding a receipt by photo via the individual transaction’ does not store a photo in the photo roll? I.e. no backup. Revolut support say this is iOS related

Please read this (below). It should be stored locally.

I had read that but on my standard iPhone 6 with latest ios11 it is not other than in the app itself. Ie I have no backup in photos?