I have this happen every single session I am using the vector brush, making the operation unusable as I have to constantly re-do work I lost because I don't save every few seconds. A bigger problem is that this happens off the CTRL+Z keys, or Ctrl by itself which is unfortunately, half the shortcut for saving anyways. The screen becomes unclickable, however the program is still running. Clicking or attempting to close Affinity Designer causes the windows error sound, which indicates to me a hidden popup. However there is no way to get back to the document without killing it in the taskmanager, which does not read it as unresponsive.
Windows 7
AMD Radeon R9 200 4GB
Intel Core i5 3.40 GHz
8GB Ram