Interface Cast nodes appear to be returned as valid and context sensitive for every possible pin, even ones like floats and integers. Following the repro above, it is easy to place a node but it will never compile. These cast nodes pollute the global namespace and make it harder to find valid function calls
Interface cast nodes should only show up for Object and Wildcard pin types. CustomStructureParam seems to cause the same issue, but that might be unrelated
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-107570 in the post.