Repro Steps:

1) Create a Page
2) Using the Path tool, draw a fully-enclosed triangle.
3) Using the Path Selection tool (A), select one of the triangle's anchor points.
4) Ctrl+Click it to convert the point to a curve
5) In the Path Point's Properties Panel, change the mirroring mode from "Mirror Angle and Length" to "Mirror Angle"
6) Drag one of the anchor point's handles to a new position.

Observe how the mirroring mode reverts back to "Mirror Angle and Length.

7) Leave the mirroring mode as "Mirror Angle and Length", and drag one of the anchor point's handles to a new position.
8) Now set the mirroring mode to "Mirror Angle".
9) Drag one of the anchor point's handles to a new position.

Observe how the mirroring mode selected is now conserved and the anchor point handles move accordingly.

Expected Results: Changes in the anchor point mirroring mode takes effect on all anchor points regardless of whether it has been manually moved beforehand or not.

EDIT: After conversation today, we have elected to remove the Alignment Properties for elements inside of a Canvas. I would probably opt for giving them a 'disabled' state rather than hiding them so that users don't wonder where they've gone. Ideally, I'd love to see this accompanied by a tooltip stating 'Elements cannot be aligned within a canvas'