[Zubersoft]

That's probably due to the special mode that is used when annotating that allows you to write in real-time with the stylus. That mode basically disables the screen refresh (so nothing on the screen will update regardless of what the app is doing), but flips the pixels under the stylus to make it appear like you are drawing with no delay. The problem is that if I do something like update the state of undo/redo, that won't show up while that mode is active. Onyx's library does not make it easy to just update certain parts of the screen, and in fact, when I've tried to create workarounds to handle these issues, their library can often crash the device, requiring a reboot. 

If you prefer, you can tap the circle at the top left and then tap "Stylus Mode" to stop that special drawing mode. You will then notice the increased latency while drawing, but none of those other issues will be present. I will continue to work to improve the experience with the stylus by leveraging Boox's library, but unfortunately their SDK is lacking in many ways and has caused instability on many devices. 

As a side note, disabling "Draw highlights behind content" is a good idea if you are encountering any kinds of performance problems. That feature requires a lot of extra processing and it doesn't work that well on the Boox. Hopefully you aren't relying on highlight annotations on an e-ink screen anyways...

Mike