This can also be observed in the tablet tester, that the mouse move events are not sent during a stroke, but only the mouse down and up events are sent. Here is the thing, if the widget handles tablet events and the QPA decides it should synthesize mouse events instead of letting Windows do it, it needs to do it for the whole stroke from start to finish (or until the pointer has been cancelled) by tracking with a flag, not by relying on whether the subsequent QTabletEvent's are accepted or not.
Note: This issue appears to also cause dragging dockers with stylus to behave erratically. The dockers don't move until the stylus is released.
A possibly relevant merge request was started @ https://invent.kde.org/graphics/krita/-/merge_requests/1047
Git commit e3a74996834a637092d89c9d15d723376f909ffd by Alvin Wong. Committed on 10/09/2021 at 07:59. Pushed by alvinwong into branch 'master'. Add Qt patch to make mouse events from WinInk complete A +87 -0 3rdparty/ext_qt/0052-WinInk-Synthesize-mouse-events-for-full-pen-stroke.patch M +1 -0 3rdparty/ext_qt/CMakeLists.txt https://invent.kde.org/graphics/krita/commit/e3a74996834a637092d89c9d15d723376f909ffd
Git commit a60e51b08eae3f9706f6e58594be58a204e92bda by Alvin Wong. Committed on 10/09/2021 at 08:00. Pushed by alvinwong into branch 'krita/5.0'. Add Qt patch to make mouse events from WinInk complete (cherry picked from commit e3a74996834a637092d89c9d15d723376f909ffd) A +87 -0 3rdparty/ext_qt/0052-WinInk-Synthesize-mouse-events-for-full-pen-stroke.patch M +1 -0 3rdparty/ext_qt/CMakeLists.txt https://invent.kde.org/graphics/krita/commit/a60e51b08eae3f9706f6e58594be58a204e92bda