Precision M5510 self wake up from standbay

My precision M5510 (Ubuntu) randomly self wake up from sleep. This is a big problem because if it wake up in my backpack it will burn itself.

After some experiment I noticed that if I put the notebook to sleep (suspend) with the lid opened, it doesn't wake up if I press any keyboard key but If I press the touch pad the notebook wake up from sleep.

So I want to ask if is normal for this notebook to wake up from sleep by touch pad.