Select all in an isolated group selects and allows to move locked and hidden objects
Imagine a group. Let's isolate it and hide one object, lock another, and leave the third one as it is. Ctrl+A to select all and then move the selection. Illustrator then moves all the objects, despite it does not behave like this on canvas.
If you check layers, you’ll see that Illustrator targets all children (double circle markers) but not a parent (the recent fix), and selects all objects including the parent (big square markers).
If you try to move the selection, all objects get moved.
This is not what happens if we try to select objects on canvas, locked and hidden objects are ignored. Polls about expectations with further private questionings I made tell that some users are aware of it, and they are mostly power users that discovered it long ago, but most users expect locked/hide objects to stay in place — approximately 2 to 1.
There is another case that has a similar behaviour — artboards you can move and have objects on them moved as well, despite them being locked or hidden, and there is an option to toggle that — 'Move Locked and Hidden Artwork with Artboard' in Preferences > Selection & Anchor Display. We can target/select the isolated group and get a proper selection, but Ctrl+A still select everything, like the attached images shows.
Treat groups as a box: we open it (= isolate) and want to deal with things with it. Yep, we can move the opened box, but this is not the reason we open it, right?
roma krivenko commented
I think that there is a mixup of entities. The purpose of hiding is to prevent selection and the purpose of locking is to prevent movement.
A group should not behave itself as an artboard. The artboard is a part of a canvas or parented canvas itself and should inherit its behaviour. E.g. anything locked on a canvas or an artboard should be locked absolutely. You can move the artboard and locked object moves with it because now artboard is a canvas for all objects inside it. And there is a nice and logical feature that allows move artboards with or without content.
The group on the other hand can only contain objects that relative to each other and if we apply an attribute that implies absolute positioning the group should not change this attribute. E.g. all objects except for the locked ones can be moved either by moving the whole group or by selecting all objects inside the group.
The problem with the hidden object is again because it should not be selected at the first place even by select all operation. Because it ruins the logic of hiding anything.
Another report that shows Ai selects hidden text objects:
A related and solved issue about ways of selecting locked/hidden objects on a layer: