I've done some more investigation.
The example I gave is not actually an example of the overspill - which I have seen on another example (I'll dig that out at some point and post it).
However, what I do notice with this (above) example is that the mesh surface generation with "interpolate" (the default) generates surfaces that just don't exist in the dense cloud. In the example shown, the mesh is being extended past the bottom of the skirt and also past the edge on the left hand side where there are no dense cloud points. These mythical surfaces then get other parts of the photographs projected on them when texturing is done. When I generate the mesh with no extrapolation or interpolation the result is correct (albeit with all the holes not filled in).
One aspect of these examples is that the photos are mostly taken from above, with very foreshortened views of the vertical sides of objects. My intention is to generate overhead views, so I'm not too interested in missing detail from the sides of objects. This all works fine except for those non-existant surfaces that are being generated.
A work-around for my case is to use height field generation. This does produce a "correct" result, but I would have thought surface generation in the normal, arbitrary, way would produce a correct result too. I don't know much about how meshes are generated from point clouds, but I find it surprising that the algorithm would construct surfaces that have no points to be constructed from!