wifi signal strength shows extremely strong when it's going to lose connection

[Evan Wang]

$ system-image-cli -i
current build number: 9
device name: arale
channel: ubuntu-touch/rc-proposed/meizu.en
last update: 2015-06-01 10:31:33
version version: 9
version ubuntu: 20150529.1
version device: 20150522-a851049
version custom: 20150529-722-5-31

Steps to reproduce:
1.Connect to a wifi
2.Move the device out of range
3.Check the wifi signal strength before it's going to lose connection

Expected results:
The signal strength should become weaker and weaker till lose connection

Actual results:
The signal strength became extremely strong before it's going to lose connection

Additional information:
 Checked the access point before and after the signal strength became strong,
==>before
$ iwconfig | grep "Access Point"
Mode:Managed Frequency:5.18 GHz Access Point: 9C:D3:6D:A3:B2:E7

==>after
$ iwconfig | grep "Access Point"
Mode:Managed Access Point: 00:00:00:00:06:00 Tx-Power=off

 The access point did not change immediately when wifi signal strength is showing extremely strong, need waiting for about 1~2 seconds, then after a while, wifi is disconnected.