Why does it show tags that don't exist?

Question

This has happened to me many times. For example, I was writing a question about Hoopa and Volcanion. In the "example tags" area there was a tag for Hoopa and a tag for Volcanion. I clicked on these, then when I tried to post the question it said those tags didn't exist. Why does it show tags that aren't real?
Here's a screenshot: Screenshot

Comments

Can you post a screenshot of the error?

Also, those tags do exist:
http://pokemondb.net/pokebase/tag/hoopa
http://pokemondb.net/pokebase/tag/volcanion

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Does the same happen if you put "hoopa" all in lowercase?

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Yes it does