If I move the Powder Toy window on my mac with OSX Mavericks my mouse becomes offset from the brush. I also have the average issues that have plagued TPT on Mavericks with stamps, login and the message about installing TPT.
I have 89.0 and am using a MacBook pro 13in. retina with 10.9
This bug is a major issue for me because the window opens in the middle of my screen and for TPT to work I need to leave it where it is when it opens.
Works for me. (I also have the other average issues, but moving the screen doesn't cause any extra bugs.)