Al', I can't answer your specific question but here's an example of the sort of nonsense insurance can be.
A few years ago my garage was broken in to. The two items taken were a chain saw and a 2hp. Outboard engine.
The insurance replaced the chainsaw, but refused to do the same for the outboard. The excuse being the engine should have been on a separate marine insurance.
I argued that they were both in the garage, so why one and not the other? ....."Sorry, but rules is rules!"
There is a common insurance rule which states any outer door must have at least a 5 lever, insurance approved, security mortice lock fitted, so just how one could be fitted to a shed door I don't know.
I would suggest, therefore that if the shed was broken in to and inadequate locks, or worse none at all were fitted, the contents might not be covered.
I too would be interested in the responses to the question.