Tidus should have his japanese name.

Near as I can tell, Tidus is the only Final Fantasy character whose tag uses his english name instead of his japanese name. Looking at the tags you have Frioniel, Tina Branford, Butz Klauser, and... Tidus. Now, I'm not sure of the official spelling of his japanese name, whether it's Tiduh or Tida, but it's most definitely not Tidus.

If Bartz has to be Butz, then Tidus can't be Tidus.

It would be Tiida, except Japanese sources list his name as Tidus.
Here's a CD from before the English release of FFX.

Here's a later example from FFBE

Ah, I see. So it's the official sources that make no sense. My mistake.