"Hidden" GCDs need to GO...

[Vstarstruck]

Are you hitting your OCGD fast enough after the first CGD? Everyone should be able do one without clipping unless they have really high ping. Usually it is doing 2 OCGDs while in GCD is what people complain about and that it is super hard to have a low enough ping for.

This comes down to animation frames/locking and how slow the server is to respond. See also: Being able to move at the tail end of a spell cast and still have it go off, and being out of AoE telegraphs before they completely finalize but still getting hit because the server resolved the attack before your position was updated.

With practice, you'll get used to it.

You can get used to it and deal with it sure, but it is a flaw of the game and warrants being talked about for a suggestion of change and improvement.