The back and home button of Asus tablet of mine malfunction, I seen many info people saying about rebooting and factory reset, but I find those step are annoying and somehow discovered this simple method to put the button on again:
1. Press volume button ( either increase or decrease few times, wait for a few seconds )
2. Press the home or back button afterward.
Do note this method I used might not persist permanently but I had it ok for most of the time. Hope it helpful, have a great day >_<
Also I personally think the interchange overlap of the browser of the tablet somehow counter reacted with the tablet built in interface because mostly the same problem occurs when I re open several tab at once :-P