I left it in the garden and returned to move it a few weeks later and the feeder was full of water.
The fault lies in the design. The lip that is present in the other boxes (brood, super, floor) is missing from one edge, where the feeder lid is. See below. You can see bottom right where the lip finishes.
The solution is relatively easy. The run-off cut-out on the roof (see below) needs a chute adding to channel the water off the roof and prevent it from running down, past the missing lip, and into the feeder.
It's not that easy to see in the photo, given my brilliant (!) camouflage painting, but you can just discern the cut-out in the centre of the photo.
I shall be on to the vendor and report what they say.