Question by example: There is the c++11, and c++0x is a synonym for it.
I recently noticed that when I filter for questions with the c++0x, the synonym doesn't go "backwards", i.e. I only see those old questions that were genuinely tagged c++0x. I had to filter for c++11 explicitly to get both the old and the new questions.
Why do synonyms work in this arguably surprising way? Me, I hadn't paid much attention to the fact that someone replaced the old tag by the new one and made a synonym, and I certainly didn't expect that I'd have to change my filters. After all, such tag changes aren't reported in a way I can easily scan and absorb.
So, would it be sensible to make all synonyms behave entirely equally, so that filtering by any one of them selects everything matching any synonymous tag?