Hi Igor
I noticed a strange behavior regarding the mask usage.
Depending on how you go about it, if you invert the mask (change to negative) you either get a completely black view or you have the opposite of the mask that is displayed.
Attached a little project and the procedure to reproduce the issue is :
Procedure 1:
1) Adding an blank mask
2) Put the Macaon mask into the mask stencil
3) Put the photo of the Macon in the content of the mask
4) Added the Color correction -> Negative modifier on the mask
Result: the entire view is black
Procedure 2:
1) Adding an blank mask
2) Put the Macaon mask at the same hierarchical level as the mask container
3) Added the Macaon photo at the same hierarchical level as the mask container
4) Drag and drop the Macaon mask into the mask stencil
5) Drag and drop the Macaon photo into the mask content
6) Added the Color correction -> Negative modifier to the mask
Result: the mask has been inverted
Negative-mask.zip