This might well be characterised as a (dubious) feature rather than a bug - but I’m sticking it here as it nearly had a bad consequence for me.
When amending a standing order, the reference field resets to (I think) the last used reference for sending to that account, rather than the reference that the transfer has been set up for.
(I found this out when I tried to change a bunch of standing orders from the 1st to the 31st. The references were all mixed up - ultimately no harm for transfers to myself, but when it’s to third parties that use the reference to route payments then money could go astray).
Details to reproduce:
Change the date of a standing order on an account with multiple saved references.
OnePlus 7 Pro