Sometimes the IDE shows Yún, sometimes not

I have installed Arduino 1.5.5 on my computer. My operating system is windows 7 64 bit.

I have an strange issue:

Sometimes when i open the Arduino IDE I can see the Arduino Yún IP in tools/port (like opcion.jpg). However if I close the Arduino IDE and reopen it, the Arduino Yún IP dissapears and I can’t see it anymore even I close and reopen several times the IDE (like opcion2.jpg).

Did you have a similar problem and how did you resolve it?

Same here, so I'm very curious as what the solution is. :)