Removing and then attempting to add a class back onto canvas fails

[afawcett]

This issue relates to the unreleased v1.6 version.

1. Place some classes on the canvas as normal.
2. Deselect one of them
3. Attempt to reselect the same one

Expected Result: It is added again (usual top left default place)
Actual Result: Nothing is added, the classes remained greyed out and the canvas is not clickable nor items can be moved around.

Have we removed the class from the canvas correctly? Maybe worth scanning the samples in the original repo for the library? https://github.com/christophevg/UmlCanvas