But thanks for the report :)

I think you misunderstand me. Applying works, but isnt a solution where the curve object should keep the object mode rotation. For example to trick the twisting.

Keep in mind that new creations first use the Grid Floor Scale or the last radius you have set it up to determine the circles radius. Lets say I have it at 0,05 - then this is the curve I will start with:

I still don't think we have a bug here, it's more like you want it to work this way, but essentially everything works fine. I'd like to get input from a more advanced user than me though ;D @ronan ducluzeau (zeauro), does this look like a actual bug for you? Or do you have a workaround or such?

The workaround is to use scale operator of edit mode instead of this setting.
It is probably what are doing most of users that did not notice the problem.

But obviously, the setting does not work as it should, as expected when you have already use it in edit mode for meshes.

I mean what is expected is a scale of primitive that preserves its shape.

May i ask to reopen this case?
Workaround is easy and not really a problem, only sort of annoying. But as zeauro pointed out, this is not consistent to mesh setting.

Compare this to a Plane mesh - its flat and Z could be ignored for the radius setting but works fine in any rotation.