artefact, you’re very welcome, please have a look at the screen capture, done in R19 for you.
Can you reproduce the steps? I create a cube, shrink wrap it to a sphere and then use the Pen Tool.
You might download the clip, for a better viewing experience.
I hope that makes it work for you.
You also can use the “Object Manager> Object> Current State to Object – while in Object Mode and the Object in question is active. This should give you a copy to work with. Which can be deleted afterwards.
Alternative, drag the shrink wrapped object under a Subdivision Surface with the setting of zero for the subdivision. This creates an internal non editable copy of it as well.
For both, have a look here: