I notice something,when I am using my wireless keyboard to type something the pointer of my magic mouse disappears ,but the minute I start using back the magic mouse it reappears ,when I am watching full screen videos the pointer diappears but when I finish watching videos and I start back using the magic mouse it reappears ,to me I think it is perfectly normal it does this ,except for one thing ,somethimes the magic mouse pointer would not reappear ,if you check the battery and the bluetooth connection ,the magic mouse would still be connected,what worked for me was when I turn off the magic mouse and put it back on.Another method is if you use command and shift it would reappear.This is an apple issue and it has to do with a bug ,it's not your mac or your mouse or the bluetooth connection or mouse batteries ,apple needs to give a software update to fix this ,I hope they do soon because they are really sticking on this one.