I'm calling this a bug, because it has really been bugging me. It's infuriating.
When you use the Node/Pen tool to make a path, it creates a layer called Curve.
When you use the Ellipse tool and create a shape it makes a layer called Ellipse. You can click the 'Convert to Curves' button, to change it to curves and it changes the layer name to Curve.
So you would expect these two layers to behave the same way. Well no.
For example, trying to use the Pen version as a mask is extremely difficult. It behaves differently when nested, e.g. you cannot apply Gaussian Blur via fx, to the 'edge' of this mask. Instead it is applied everywhere (inside as well as the edges). Again with the Gaussian Blur fx ... if you are using the Pen version as a mask and are using Blend Options ... when you apply Gaussian Blur fx, the image (that you're masking part of) is suddenly filled at 100% ... so it is obstructing/cancelling the Blend Options (presumably because it can't apply the fx to the edge alone). It also doesn't mask correctly when nested, instead it just blanks out the layer completely.
I feel that the behaviour of layers with a single name, should not vary according to which of two tools was used to make it.
Took me the last 3 hours to work out what was/is going on. Sigh ...