So guys it would be nice if someone step up and fix this annoying bug, your help is greatly appreciated!
About the future of MyPaint well this is just an opinion, a speculation from experience. With MyPaint migrate to gtk-3 thus using pygi (and possibly python-3), It would be most tedious migration I've ever seen before for Windows platform, I meant where is PyGI now? Not even a release yet... and GTK-3? usable but not ready. Lets just hope Windows get some priority in the upstream sooner.
The dreaded question is how gtk-3 handle tablet this time? with gtk-2 there are many users complaining about their tablet which likely gdk<->wintab issue and since gtk is a gnome project (a dominant linux GUI), priority for other platform is somewhat lower than other cross-platform GUI. In the past decent releases has been fewer too. From interface point of view, last time I checked (gtk 3.4.4), it's already native themed but I can't made it work with mypaint since my experimental pygi build can't deal with gtkbuilder (maybe because I use 64bit off_t and time_t which is ABI breaking?). Anyway it still a bit early for pygi in windows...->
This build here is a manual build and unlikely I will maintain that build environment anymore.
Test and report bugs! your reports are very valuable in the release process, I believe the lag bug is workaround-able.