Emulator is already running but not able to see it in ubuntu

Emulator is already running but not able to see it in ubuntu

I am using ubuntu 12.04,and Eclipse Platform Version: 3.7.2, I have one
issue which i observed occasionally on my system I dont know whether this
issue is common and did't find any related question so asked.. problem is
- "when I tried to launch android application using emulator(API level 17
Nexus 4),it runs fine no problem and emulator is in front of me, But the
moment i open other window like browser,editor it hides and i am not able
to see it.." Log says that emulator is ruuning but dont know where it
hide.