I don’t know if it was added in an update, but it seems like I frequently delete things on other frames when I don’t mean to. This is because if you:
Box select something.
Select a different layer. (Very common after realizing you’re on the wrong layer)
Hit delete.
It will delete that spot across all frames on that layer. The problem is that you might not even notice that it happened until you cycle through the other frames.
As far as I can see, other frames should only have data deleted if you select them. Clicking on a layer is far too common.
I think this is intended behaviour, and it’s been like this as long as I can remember.
Selecting a layer selects all the cels in it, because that’s what a layer is. It sounds like what you want to do is select one cel on a different layer, rather than a layer. Using the up/down arrow keys instead of the mouse might help you build a better habit of selecting just the cels you need rather than the whole layer.
I agree that it would be good to have better indications of when you may have done this, though. Aseprite lets you display cel thumbnails in the timeline and they would make this more noticeable, but they also make the timeline unwieldy, especially for larger animations. An opt-out warning for selections deleting from multiple cels at once could work.
I think that clicking on a layer should select the same frame that you’re on. I don’t really see any reason why selecting a layer should select all cels in it. There’s very few situations where I ever want to delete something on all frames, since animations move.
I actually disabled the arrows, because I kept pressing them by mistake when trying to move selections. Since pressing the down arrow while not within the current selection area would change the cel, which I rarely ever wanted to do.
I think it would make more sense to have a command to select all cels if you right click on the layer. The amount of times that you want to delete a super specific area on all cels is pretty rare.
this is not a bug.
the reason is that it is convenient. when you want to select all cels in the long timeline to transform them all at once, this is the only acceptable way. i personally like this behaviour.
and aseprite does show you that you have selected everything.