Yeah, you really need to think two steps ahead and write out specifically "My problem is Y and not X, and the difference is ..."
I find good success writing in my question "question is similar to <already answered question> except I need this and that, which that solution doesn't provide"
I meant it the other way. I encounter so many questions on SO, where the problem was X after all. And then X gets solved, everyone is happy. Besides me, who gets it as a search result for problem Y that no one, including the OP, actually was interested in solving.
I find good success writing in my question "question is similar to <already answered question> except I need this and that, which that solution doesn't provide"