Digital Light & Color

Something to consider.
If you select multiple transformations and then click Close selected transformations, you get the confirm message warning for each selected (checked) transformation. When you have a long branch and want to close around 10 transformations, you have to confirm 10 times the same message.
I think one message could be enough for each uninterupted group of selected transformations. In case of a gap in the selected transformations there might be another message if necessary.

Normally, you only have to confirm once. I believe the only time you need to confirm multiple times is if you are closing transformations that are inputs for some other transformation, but maybe I am missing something.

Some of the transformations did have masks attached to them, but not all of them. I will find out.

The problem should not be the mask but if a transformation not being closed depends on a mask from one of the closed transformations or if a transformation not being closed uses one of the closed transformations as an auxiliary input (e.g. a Layout using one of the image in a panel) or a Compare or Composite referring to one of the closed images. If you see the message again, please let me know what it says.

I think I have found it.

It happens when a transformation anywhere below those checked for closing is used as an auxiliary input in Composite. In this case the Composite is in another branch.
It happens even if the this [auxiliary] transformation is bypassed.

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Then it goes like this:

First message asks for confirmation to close the "n" transformations

Then follows the warning message for each checked transformation:
Closing the selected transformation will change one or more inputs or masks in the transformations.

After the message for the last checked transformation is OK-ed, the checked transformations are closed in one step.

OK thanks, will check it out.