Fahmy,

Its a bad design. If noise gets coupled into your EA pin, your CPU will strike off on its own to unknown places.

Here is a test for you:

Imagine a member of your family is on life support. Their machine is run by your processor. There is a thunderstorm outside.

Would YOU trust it ?

It must be tied. The Atmel works fine for me with it tied high, and I can manipulate the lock bits too.