Why whenever I enable the WiFi interface NM sends a DHCPDISCOVER if still not associate with any AP?

[Stolz <stolz ya com>]

Whenever I switch from wired to wireless interface, it takes more than
45 seconds to get the wireless interface enabled. Looking at the logs,
seems the problem is (k)Networkmanager sends a DHCPDISCOVER before
been associated with any AP:

Feb  7 18:03:58 vostro NetworkManager: <info>  DHCP daemon state is
now 1 (starting) for interface wlan0
Feb  7 18:03:59 vostro dhclient: DHCPDISCOVER on wlan0 to
255.255.255.255 port 67 interval 3
Feb  7 18:04:02 vostro dhclient: DHCPDISCOVER on wlan0 to
255.255.255.255 port 67 interval 7
Feb  7 18:04:09 vostro dhclient: DHCPDISCOVER on wlan0 to
255.255.255.255 port 67 interval 8
Feb  7 18:04:17 vostro dhclient: DHCPDISCOVER on wlan0 to
255.255.255.255 port 67 interval 10
Feb  7 18:04:27 vostro dhclient: DHCPDISCOVER on wlan0 to
255.255.255.255 port 67 interval 10
Feb  7 18:04:37 vostro dhclient: DHCPDISCOVER on wlan0 to
255.255.255.255 port 67 interval 9
Feb  7 18:04:42 vostro NetworkManager: <info>  Device 'wlan0' DHCP
transaction took too long (>45s), stopping it.

I'm not a network expert but, AFAIK, if you are not associated with
any AP, there is no link so sending a DHCP petition makes no sense for
me. Can someone explain me this behaviour? It's annoying having to
wait almost a minute every time I want to use WiFi.

Thanks.