image data still stored when image is saved with layer mask

[discordian_owl]

I am not really sure if it's a bug at adobes pov but for me it is.
The scenario is the following: I have an image that should get a transparent area. When I select this area in photoshop, use a layer or vector mask (doesn't matter) and save/export the image (tested with "saved as", and "save for web") as *png I noticed that the filesize is quite big or even the same as without the mask - which shouldn't be the case since I have less image data. When I upload or view the saved image in a file explorer, everything seems fine (except for the file size), the transparent space is as it should be BUT when I use for example PHP (or similar tools) to render the image I suddenly receive the whole image without an applied mask, meaning that the transparent area is not transparent anymore. This explains the big file size - the image data is still there.
When I don't use layers and destructivly remove the area it works like it should. The file size is smaller and the image is rendered correctly in PHP.

Version/App: Tested Photoshop CS6 and current CC 2022 (windows).
Test-File: Doesn't matter. Tested it with multiple images on two different systems, result is always the same.
Expected result: The moment I hit "save" all layered masks should be stored in the same way as if I used a destructive method. Resulting in no "hidden storage" inside the file and just the plain image as I see it. Yeah, there is stuff like meta-data that is also stored but that's nothing in terms of filesize and at least I have options to store/delete them when saving.

If this is no bug but an intended feature I wonder what's the point of it. When I re-open the saved (faulty) *png I have no way to return the mask because it's a plain *png. Additionally I have this large file size that can be huge, depending on the area I cut out. I really see not benefits for the user but the opposite.

[Jeff Arola]

After the layer mask is applied you need to make a selection of the object by ctrl or cmd clicking on the layer thumbnail in the layers panel, then Select>Inverse and Edit>Cut or Clear.

[discordian_owl]

Well, that's what I mentioned in my post above. This is a destructive method and it works as a workaround but I already knew this 🙂
1) what is the point of using a destructive method after a non-destructive method that doesn't change anything visually?
2) It doesn't change the fact that this behavior is a bug since it's not something the user would expect or want (as also described in my post).

You could however explain to me why this isn't supposed to be a bug.