On the ZD and SZ you can enable 802.11r which caters for PMK and OKC when using 802.1x..
This wont solve the issue if your clients don't support 802.11r i.e. iPhone 4, iPad 2nd Gen etc.
Note: On the ZD platform you also get the use of 802.11k to assist with client roaming, but as above you have client restrictionsIf you have 802.11r enabled you will see MAC FLAP on your network, don't worry about this, as this is normal behaviour and you can just disable the reporting of the MAC FLAP on your switch/ router (providing its Cisco), by using the following command
no mac-address-table notification mac-move
See command reference for further information:
http://www.cisco.com/c/en/us/td/docs/ios/lanswitch/command/reference/lsw_book/lsw_m1.html#wp1142649