Why you do dis, Mum?

Back in June I posted a photo of the loco at the Zig Zag railway, apparently taken on Mum's birthday, because that was the date she'd written on her print.  

Except it wasn't on her birthday.

The other week I was scanning Dad's slides of the trip.  All of them from that day were labelled the 22nd June.  For some very very strange reason (why, Mum, why????) she'd crossed out the date on just that slide and written her birthday on it.  Why why why? :)

Why you do dis Mum?