My version is 3.8.99. Anyway Here is the problem:
As you can see that orange key didn't change no matter what I try to hide the attachment image in the first keyframe. It keep return back to unhide and become orange again.
The bug happen quite frequently. It usually occur after I copy a whole slot along with their old keyframe.

You can check out the test project in the attachment file to see for yourself.

Okay I see the problem,
When I copy a sloth with 9 images inside along with their keyframe, with the new sloth which I delete 8 unnecessary images.
But the Spine didn't delete their key frame along with the deleted images. And those orange key frame exist as the same name as the last attachment image.(like a soul without a body to possess)
I guess the Spine can be improved with this case: when I delete an attachment image, all of its related key frame should be auto removed too.

Nate wrote

Thanks for reporting this! Any time you see orange keys when you haven't changed anything, it means there is a bug we would like to fix.

We've made the next 4.0 release (4.0.82-beta) clean up projects that have this problem. When your project loads, you'll see some warnings that duplicate timelines have been removed.

I wasn't able to figure out what steps you took in 3.8.99 to cause this problem. I'd like to know so I can try it in 4.0 to be sure it is fixed there. Can you try the steps in 4.0 and verify the problem does not happen in 4.0?

The way I made this bug occur is quite simple.

• For example: a slot with 9 attachment images , each image have their own key in the animation
  =>Then I copy that slot and say "yes" when Spine ask me if I want to copy all of the key of that slot too.
  => We have a new slot now with 9 attachment images and their key frame look exactly like the old slot.
  => Then I delete all 8 attachment images of this new slot. At this point I guess we 'll have 8 duplicates time line using the same name as the remain image.
  The error occur because the Spine didn't clear up all the key of deleted attachment images.

How can I update from 3.8.99 to 4.0 anyway?