This seems like a problem with DHCP (this is on an unencrypted network):

Oct  9 12:07:32 acer dhclient: Internet Systems Consortium DHCP Client 4.1-ESV-R4
Oct  9 12:07:32 acer dhclient: Copyright 2004-2011 Internet Systems Consortium.
Oct  9 12:07:32 acer dhclient: All rights reserved.
Oct  9 12:07:32 acer dhclient: For info, please visit https://www.isc.org/software/dhcp/
Oct  9 12:07:32 acer dhclient: 
Oct  9 12:07:32 acer NetworkManager[915]: <info> (wlan0): DHCPv4 state changed nbi -> preinit
Oct  9 12:07:32 acer dhclient: Listening on LPF/wlan0/00:23:4d:38:09:45
Oct  9 12:07:32 acer dhclient: Sending on   LPF/wlan0/00:23:4d:38:09:45
Oct  9 12:07:32 acer dhclient: Sending on   Socket/fallback
Oct  9 12:07:32 acer dhclient: DHCPREQUEST of 192.168.1.79 on wlan0 to 255.255.255.255 port 67
Oct  9 12:07:33 acer dhclient: DHCPNAK from 192.168.1.75
Oct  9 12:07:33 acer NetworkManager[915]: <info> (wlan0): DHCPv4 state changed preinit -> expire
Oct  9 12:07:33 acer dhclient: DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 3
Oct  9 12:07:33 acer NetworkManager[915]: <info> (wlan0): DHCPv4 state changed expire -> preinit
Oct  9 12:07:33 acer avahi-daemon[734]: Joining mDNS multicast group on interface wlan0.IPv6 with address fe80::223:4dff:fe38:945.
Oct  9 12:07:33 acer avahi-daemon[734]: New relevant interface wlan0.IPv6 for mDNS.
Oct  9 12:07:33 acer avahi-daemon[734]: Registering new address record for fe80::223:4dff:fe38:945 on wlan0.*.
Oct  9 12:07:36 acer dhclient: DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 8
Oct  9 12:07:42 acer kernel: [ 2265.920079] wlan0: no IPv6 routers present
Oct  9 12:07:44 acer dhclient: DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 11
Oct  9 12:07:55 acer dhclient: DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 19
Oct  9 12:08:14 acer dhclient: DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 19
Oct  9 12:08:18 acer NetworkManager[915]: <warn> (wlan0): DHCPv4 request timed out.
Oct  9 12:08:18 acer NetworkManager[915]: <info> (wlan0): canceled DHCP transaction, DHCP client pid 3878

dhclient sends a request for .79 (I'm assuming this is its last known dhcp address), which is denied by the server on .75. The client then sends a DHCPDISCOVER which should be replied to by a DHCP offer by the server, but it never is, so the discovery times out.

A manual address setting works, so it does seem to confirm this. If there is nothing wrong with the server, my thoughts would be that there is something wrong with the discover packets (malformed maybe), or something is eating up the offers on route back from the server.

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Also, a WPA-PSK TKIP network:

Oct  2 20:03:36 acer dhclient: Internet Systems Consortium DHCP Client 4.1-ESV-R4
Oct  2 20:03:36 acer dhclient: Copyright 2004-2011 Internet Systems Consortium.
Oct  2 20:03:36 acer dhclient: All rights reserved.
Oct  2 20:03:36 acer dhclient: For info, please visit https://www.isc.org/software/dhcp/
Oct  2 20:03:36 acer dhclient: 
Oct  2 20:03:36 acer NetworkManager[912]: <info> (wlan0): DHCPv4 state changed nbi -> preinit
Oct  2 20:03:36 acer dhclient: Listening on LPF/wlan0/00:23:4d:38:09:45
Oct  2 20:03:36 acer dhclient: Sending on   LPF/wlan0/00:23:4d:38:09:45
Oct  2 20:03:36 acer dhclient: Sending on   Socket/fallback
Oct  2 20:03:36 acer dhclient: DHCPREQUEST of 192.168.1.22 on wlan0 to 255.255.255.255 port 67
Oct  2 20:03:37 acer wpa_supplicant[990]: Michael MIC failure detected
Oct  2 20:03:37 acer wpa_supplicant[990]: WPA: Sending EAPOL-Key Request (error=1 pairwise=1 ptk_set=1 len=99)
Oct  2 20:03:37 acer wpa_supplicant[990]: Michael MIC failure detected
Oct  2 20:03:37 acer wpa_supplicant[990]: WPA: Sending EAPOL-Key Request (error=1 pairwise=1 ptk_set=1 len=99)
Oct  2 20:03:37 acer wpa_supplicant[990]: TKIP countermeasures started
Oct  2 20:03:37 acer kernel: [ 7529.682694] wlan0: deauthenticated from 00:18:4d:7e:06:84 (Reason: 14)
Oct  2 20:03:37 acer kernel: [ 7529.704466] wlan0: deauthenticating from 00:18:4d:7e:06:84 by local choice (reason=14)

Michael MIC failures from wpa_supplicant.