Mmmm, it just seems to be working today, not sure why it's different, I haven't changed anything.
I think I realise why this happens, but is there a way to avoid having the operator click outside of the fields, before creating a new record in the portal.
Clicking outside the fields is the same as performing the script step: Commit Record. Until the record is commited, the auto-enter actions in the related records will lookup the previous values in your record. You can set up script triggers that perform a commit record with On ObjectSave or OnObjectExit if you want.