NM+WPA_Supplicant+Systemd trouble: can't connect to WLAN

[Nickolai Dobrynin <ndobrynin gmail com>]

Dear all,

I've Googled my stomach off and tried to get help on Gentoo
(my distro of choice) forums:

http://forums.gentoo.org/viewtopic-t-998728.html?sid=87a26a7434ce0489cf77789f1377f141

Nobody knows anything, so here I am.  Long story short: I can't
get the NM+WPA_Supplicant+Systemd combo to connect to WiFi.
I depend on a WiFi for my installation and have no wired Internet access.
Everything works via DHCPCD (with NM off), but when I disable DHCPCD
and fire the NM up instead, it creates a WPA Supp instance which says:

wlp3s0: Associated to a new BSS: BSSID=88:dc:96:03:5b:28
wlp3s0: No keys have been configured - skip key clearing
wlp3s0: Select network based on association information
wlp3s0: No network configuration found for the current AP
wlp3s0: Request to deauthenticate - bssid=88:dc:96:03:5b:28
pending_bssid=00:00:00:00:00:00 reason=3 state=ASSOCIATED
wpa_driver_nl80211_deauthenticate(addr=88:dc:96:03:5b:28 reason_code=3)
wlp3s0: Event DEAUTH (12) received
wlp3s0: Deauthentication notification
wlp3s0: * reason 3 (locally generated)

This is happens in response to

  $ iw dev wlp3s0 connect <name>

which I execute manually, and the network is public and unsecured.

Since WPA Supplicant functions well with DHCPCD, this, to me, indicates
a NetworkManager-related issue.

I am seeking as much information as possible on how to troubleshoot this.
Don't know if this is relevant but my wireless driver is iwlwifi.

Many thanks.