Repro Steps:

1) Create a Page
2) Introduce a 512x512 Rectangle to the Stage, and convert it to a Path from its 'Path' context menu submenu. Leave the default visible Stroke (it will be needed later)
3) With the Path Selection Tool [A] armed, hold down [Ctrl] and click and drag one of the left anchor points of the Path to give it a curved corner.
4) Duplicate the Path using [Ctrl+D] in the Navigator, and position the two rectangles so that they are edge-to-edge in any direction. (essentially making two squares into a rectangle)
5) Select both squares by holding [Ctrl] and clicking on each. With both selected, navigate to the 'Path' context menu, and select 'Make Compound Path".

6) Through any means necessary, using the Path Tool (P), and the path Selection Tool (A), make the two squares on the Stage into a single rectangle with no visible seam in-between them (no seam = complete 'enclosed' shape).

Observe how since any enclosed shape is unable to be converted into an 'open' shape, that the Path Tool only provides the option to remove anchor points, not add them onto an 'open' anchor.

Expected Results: Distinct shapes within a Compound Path can be converted into a single shape.