Gijun Thank you for your report, but unfortunately I do not fully understand the problem you describe. Could you please explain the steps that would allow us to reproduce the problem? For example, which bones should we manipulate in our example project spineboy-pro.spine to reproduce it?

I see, too many undo states are created when dragging with a tool (and in other cases). We've fixed this in 4.2.27-beta, available soon!