Hi,
I have a simple drawing as you can see in the screencast. As you can see the ellipse gets two construction lines by default.
Additionally I created another line which is exactly at the same position like the construction line of the ellipse.
If I click the left mouse button and hold it for a while the small selection window pops up showing two times 'Sketch curve'.
But I don't know which is which so I cannot easily select the one I want.
Better would be of one of them could be called 'Sketch curve construction' then you can easily take the one you want.
Here a screencast: