Digital Light & Color

scenario 1

1. create a mask of an oval or rectangle shape and click Apply button
2. click the mask Undo the last operation then Redo.... and again Apply button
3. click the transformation dialog OK button
4. dbclick the output to call back the dialog
5. go to the Amount square and choose Edit -> no shape but a homoheneous 25% overlay
6. click the mask Undo the last operation then Redo the.... -> the shape is back
now you can repeat the steps beginning no 2.

scenario 2

The same scenario except that you undo and redo in the second cycle:

1. Create a mask of an oval or rectangle shape and apply the mask
2. click the transformation dialog OK button
3. dbclick the output to call back the dialog
4. go to the Amount square and choose Edit -> the shape is there
5. click the mask Undo the last operation then Redo the last operation
6. click mask Apply and dialog OK
7. dbclick the output to call back the dialog
8. go to the Amount square and choose Edit -> no shape but a homoheneous 25% overlay
5. click the mask Undo the last operation then Redo the.... -> the shape is back
6. click mask Apply and dialog OK
end so on

scenario 3
an alternative scenario to no 1.

1. create a mask of an oval or rectangle shape and click Apply button
2. blur it
3. add another shape and click Apply
4. undo once and redo once and Apply
5. click the transformation dialog OK button, go to Edit -> homoheneous 25% overlay
6. you can do undo and redo only one step so you do not get the blur and the second shape back

----------------

Conclusion:
Currently it seems that no matter how many steps you make to create a mask, if you include an oval or a rectangle into it, you can undo all of them only before you click transformation dialog OK button.
When you then recall the dialog and Edit the mask, you have only one step back.

------------------

This behaviour seems to be typical of the Rectangle and Oval. Freehand Outline Polygon and Spline do not seem to reproduce it, but only if not combined with the other two.

Possible explanation of that 25% mask overlay:

Unlike with the other transformations it seems to appear only with the Brightness transformation as a system default mask. It needs to be reset before starting a new mask.

The initial mask amount is 50% for amount controls that are zero-centered such as Brightness, but on reflection black is probably a better choice, so I changed it to 0% as for non-zero-centered amount controls.

But if other masking tools are used in the Brightness transformation, there is no overlay. So the Rectangle and Oval tools will definitely play some role, as described further.

Here is an update in brief:

use any transformation allowing masks (I used Brightness curve, Filter, Color Balance):

1. create three polygon mask shapes, apply, OK, dblclick output, Amount icon: edit Mask -> you get three polygons
2. do the same with rectangles or/and ovals -> you get no shapes (?)
3. click mask Undo and Redo... -> you get only one shape

Order of the shapes also plays a role:

If you first create an oval or rectangle and then add one of the others, you end up like at 2. and 3. with only one step back to history

But do it in reverse order (e.g. polygon, oval) -> you get both shapes straight away with all the history steps.

I just posted a fix for the Rectangle and Oval bug. Have not yet gotten to "Another two Mask Observations".