I have an iMac with Mavericks, and ever since I've had it, I've had this issue with Photoshop, and it appears to occur in every version I've used so far (CS6 and CC). After every 5-10 strokes, the stroke will show up on the canvas, but it won't register in my history. So basically that means I can't command(control)-z (undo shortcut) or anything like that without touching on or around the canvas again for Photoshop to recognize the old action, and then it also recognizes the new ones, so I have to delete the new ones and the old ones to just remove the stroke I did a while back. It's extremely frustrating, and I'm not sure how to fix it. I have Photoshop CC and I'm using a Mac, but the same error also happened in CS6. I've reinstalled my tablet drivers, reinstalled Photoshop, I've even wiped my whole OS and set back to factory settings but the problem remains. If anyone knows how to fix this, I'd really appreciate it.