Thanks Ernest for such a quick reply. In fact, we are using a multi-domain plugin on the site so that the new products section (Shiftbase) is available on its own domain. I just checked and the ‘true’ URL works fine, so I realise now it is the translated URL that confuses things.
Bit hacky, but it does what we need for now. Do you think I can make it work in that setup with the translated URL? Don’t worry if not, as I can see this more of a me problem that a plugin problem.