Given that the system automatically redirects you to the "correct" tag when you try to use a hyphenated/unhyphenated alternative, shouldn't this also do the same thing when the hyphenated/unhyphenated alternative is a synonym?
Tag synonyms aren't computed automatically. They are found via lookup. Here's the list of tag synonyms for Meta.SO, and you can even suggest your own if you at least 2500 rep. The same path will work on all sites for tags specific to that site. If you think
For reference, this is the description of how synonyms work: What are tag synonyms? How do they work?
The main problem here was that we just weren't checking the user-edited tag against the synonym list during tag validation. When the form gets posted it gets through validation, and if the tag doesn't match a synonym a new tag gets created.
This should be fixed now.