I actually emailed them the day before posting here and still haven't heard back so I'm happy you got a response and even happier that the response was to put them back!
I think these forms are often overlooked by researchers. Anybody with family on the 1901 or 1911 census returns would be wise to look at all the forms.
I guess I just hit lucky with the person who opened my email.
I had noticed them missing on one or two searches but hadn't noticed they were disappearing, if I'd been looking at my own family I would have noticed as I've looked at them before.
I agree they can be very useful, for example they tell you who owns the house, which in a lot of cases changes from a landlord in 1901 to the householder in 1911 because people got loans from the Land Commission to buy their farm between the two census.