Yes, this can happen when there are edges stacked up exactly on top of each other.

MoI will only target just one edge in that case, and it is pretty random which one will be the targeted one (well not random, I guess it is the newer one that will win). If the one on the unselected box is targeted then you won't be able to get the one on the selected box.

Right know edges on unselected objects are still targeted because there are some operations (for instance "on" object snap) that target them regardless of selection. I suppose I could fix this up a bit and suppress targeting of the edges of the unselected box just in the case for selection, I think that would make this work.

This doesn't come up too often in normal modeling scenarios, it's kind of atypical to need to select an edge for an operation when you have solids that are overlapping like that. More often you would be merging those solids together or something before you got around to doing an edge-oriented operation.

- Michael