Difference between "Return" and "Warp"?

[Sove92]

So it's a bugged out/beta skill that only works in some clients?

Also echoing that I'm ARR beta tester and have never heard of this skill til this thread.

It's not a beta skill. It was added in 4.15 and is for Rival Wings and serves as a replacement for the actual Return. The problem is it's bugged and works outside RW. Warp is technically just a function that hooks to Return's code and bypasses its CD and confirm prompt and giving it the added ability of working while in combat (though getting hit cancels it). There just isn't a check in place to ensure you are inside the intended area.

I'm playing on a Japanese server and first thing after trying Warp (it worked just fine for me) I told my FC guys about it. And guess what? - it doesn't work with a Japanese client! None of the guys that use J client were able to use Warp.
I even linked them this link: https://ja.xivdb.com/action/10061/warp
but for them it's just another Return with a standard CD.

Isn't it weird?

This happens because Warp and Return both have the same name in JP client and the action /ac デジョン prioritizes Return, probably because it's earlier in the list. If you put it on your hotbar with the help of EN client, it will work.

Ultimately, it's not a big bug, and probably won't see a fix until a hotfix after 4.25. Still against ToS, however.