[Solved] Applying Extrusion or 3D makes Bézier Curve disappear

[Lucster]

I don't understand. It just disappears but the handles are still showing. If I hover over the object, the cursor changes. If I click on it, it'll flash briefly but disappear just as quickly. It can be modified, skewed, moved but it stays invisible.

[cwolan]

Your Bézier curve is on the Controls layer.
If I move the curve into the Layout layer (or a new layer) and convert it a 3D / 3D rotation object,
I don't see any problem with using it.

FWIW
The Draw Guide says: The Controls layer is for control elements such as icons and
pull-down menus and is not usually used for ordinary drawing elements.