wpa_supplicant 2.6 HWMP routes no traffic

[Jeroen Roovers]

Command:
/usr/sbin/wpa_supplicant -c/etc/wpa-mesh.conf -s -i wlan1 -Dnl80211 -P
/var/run/wpa.pid -B -d

Configuration (/etc/wpa-mesh.conf):
user_mpm=1
update_config=1

network={
        mode=5
        ssid="xxx"
        frequency=2412
        proto=RSN
        key_mgmt=SAE
        pairwise=CCMP
        group=CCMP
        psk="xxx"
}

This is an IEEE 802.11s network using a kernel 3.4.112 with a modified
rt2800usb driver for the RT2870 USB wireless modules.

With version 2.5 this gives me a nicely working secure mesh network.
With 2.6 peering works, but I only see broadcast packets and no direct
communications between peers are coming through. It looks like routing
fails most of the time.

(Because reasons!) I use olsrd on top of HWMP and I can see its
network flooding using tcpdump, so that works. Simple ping tests to
other nodes fail at the ARP level, however, and actual useful traffic
obviously fails the same way. The routing tables and ARP tables show
peers as expected. Packets are sent out but apparently never received.
In the ping tests, only routing failures are returned.

Before I start a lengthy and costly git bisect session over the mesh
changes between releases 2.5 and 2.6, perhaps someone could give me a
hint as to where to start looking?

Much appreciated! Kind regards,
     jer