[mayuka]

Okay. It just seemed to work. When having hostapd started the client just disconnects after 1 minute instead of 10 seconds. After that it may reconnects or may not. Very strange indeed.

Here's my hostapd.conf file:

# Macros
iface="rum0"
ssid=test
#wpa=1
wpa_passphrase=0xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
wpa_key_mgmt=WPA-PSK
wpa_pairwise=TKIP

# Tables
# Define the MAC addresses (BSSIDs) for your accesspoints in a table.
table <myess> {
	xx:xx:xx:xx:xx:xx
}

# Global options
set hostap interface $iface
set hostap mode radiotap

# Uncomment these options to jump to the next channel every 2 seconds.
#set hostap hopper interface $iface
#set hostap hopper delay 2000

# Use multicast (according to the revised standard).
set iapp interface $iface
set iapp mode multicast

# Event rules

# Log probe requests.
hostap handle type management subtype probe request \
    with iapp type radiotap

# Log and annoy foreign accesspoints.
#
# This will be logged as well but the important thing is to
# annoy other accesspoints in your wireless territory.
hostap handle type data bssid !<myess> \
    with frame type management subtype deauth reason auth expire \
    from &bssid to ff:ff:ff:ff:ff:ff bssid &bssid

# The first de-auth example will not work with some newer stuff, like
# iwi(4)/ipw(4) "centrino", because they ignore management frames to
# the broadcast address as a countermeasure against the "void11"
# attack.
#
# hostap handle type data bssid !<myess> \
#    with frame type management subtype deauth reason auth expire \
#    from &bssid to &from bssid &bssid

# Detect flooding of management frames except beacons.
# This will detect some possible Denial of Service attacks
# against the IEEE 802.11 protocol (like "void11").
hostap handle skip type management subtype ! beacon \
    with log \
    rate 100 / 10 sec

# Finally log any rogue accesspoints limited to every second.
hostap handle skip type management subtype beacon bssid !<myess> \
    with iapp type radiotap limit 1 sec

But I still don't understand why starting hostapd changes the situation... And yes, I've read the man page several times now.