Locked and/or hidden objects still become selected
The object is locked and/or not visible, yet when the layer is selected, all objects including the locked and hidden objects become selected and move when they should not.
(Illustrator 26.0.1 / OS Catalina 10.15.7)
Vote for the the isolation bug I described here:
This behavior also does happen if you try to lock or hide an object in a group, then isolate it and Select All. 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?
Yes, it happens when you click the square marker in the Layers panel to select the layer’s children, and then they all are draggable, regardless of lock/hide state. It's an ancient behaviour.
However, if you target a layer instead (the circle marker), Ai will select only those object that are not hidden/locked (thus ready for applying effects/attributes/whatever). This is actually still quite new, an if you have older CS versions, that is not how it worked there.
So if you NEED all objects in a layer selected, despite them being hidden/locked, — use the square selection marker.
And if you DON’T need them be be selected, use the target circle marker.
Because both workflows are useful.
And I agree this is not intuitive to grasp :)