I installed Yosemite on my 15-inch retina MacBook Pro (early 2013). I have an external monitor, a keyboard and an Apple Magic Trackpad connect to it at home. In the first day, it was working well. However, since yesterday, the Magic Trackpad began having erratic behavior. I changed the batteries and it took a while to be recognized. Now that it has been recognized, it lags so much that it nearly looks like it is not even connected. I cannot use it. The built-in trackpad in the MacBook Pro works well, and an external Microsoft Mouse (USB wireless) works well as well. The only problem is with the Apple trackpad. Did anybody have the same issue? Is it a Yosemite problem?