In paint tool SAI, every time I flip the pen to use the eraser, SAI registers it as the selection tool. I've tried everything I could think of to fix it, but nothing seems to work. :c
Is it possible that in your pen tool preferences you've set the back, eraser part of your pen to be a shortkey or keyboard letter that would be the selection tool while in Sai? I don't use Sai, so i can't give you any hints on the shortkey.
Does anyone have any ideas?