Update: our german dealer provided me with a new software image. But the problem still exists:
m1 [standalone: master] (config) # show version
Product name: MLNX-OS
Product release: 3.5.1006
Build ID: #1-dev
Build date: 2016-03-09 11:29:49
Target arch: ppc
Target hw: m460ex
Built by: dvirl@fit74
Version summary: PPC_M460EX 3.5.1006 2016-03-09 11:29:49 ppc
Product model: ppc
Host ID: E41D2DE937AE
Uptime: 22m 57.660s
CPU load averages: 1.62 / 1.62 / 1.34
Number of CPUs: 1
System memory: 821 MB used / 1206 MB free / 2027 MB total
Swap: 0 MB used / 0 MB free / 0 MB total
m1 [standalone: master] (config) # show ipv6
IPv6 summary
IPv6 supported: yes
IPv6 admin enabled: yes
IPv6 interface count: 1
m1 [standalone: master] (config) # ipv6 routing
% Unrecognized command "routing".
Type "ipv6 ?" for help.
m1 [standalone: master] (config) # ipv6 ?
default-gateway Configure an IPv6 default route
dhcp Configure global DHCPv6 settings
enable Enable IPv6 for the entire system
filter Configure IP filtering for IPv6
host Configure static hostname/IPv6 address mappings
map-hostname Ensure a static host mapping for current hostname
neighbor Configure static IPv6 neighbor MAC (link layer) address mappings
route Configure IPv6 unicast static routes