I decided not to create a new incarnation of that bug (I've already submitted #1624, #1625 and 3201) but rather discuss it here. Although Andrey Simanovsky said that the root issue of this bug #1647 can be accessible now and the problem should be resolved in build 88 none of those statements apears to be completelly true :)
I can access 1647 and see the list of duplicates, but unfortunately I could not see "Discussion" - see attach.
In build 88 class from the shared source file is resolved in 2 csproj, but still unresolved in third one (which is located in the another folder). You can reproduce it if you will open solution from attachment of issue 1625