I'm uploading 1.3.26 now. This has a new undo system under the covers. This had to happen to fix undo not working and also slowdown with huge projects (200+ animations). This required massive changes, so please keep an eye out for undo related bugs. The new approach is much better and will never have problems no matter how large the project. It also cut down the .spine project file size (loading old projects always works of course).