Ian,This always used to happen to me developing software - I'd design in all the possible ways a user could run into problems, then wait for the users to find all the others!
I use that system when commissioning new machinery for work .... Thrash the life out of it to see if I can break it! ....... then hand it over to the operators and wait for them to break it (they usually do have more success than I !!!)![]()