Problems occur when cancel is pressed on feature map

[chrisala]

To reproduce:

• Draw a shape using the feature map. Press OK.
• Press the shape you just drew to edit it.
• When the map shows, press Cancel.
• Press the shape again to edit it.
• Without making changes, press OK.

Expected:

• The shape is unchanged.

Actual:

• The shape is deleted. This is because the event handler isn't removed when cancel is pressed, so the next time OK is pressed the event handler fires twice, but in between the shape has been cleared for the next use of the map.