We indeed have seen such problems on all versions of OSX not just
10.10.x.
Other things to try. You can find exact instructions for some
of these by googling.
1) Get the AP off of channels 132-144 if it is there
2) If the AP/controller can be rebooted, try each of those and retest.
3) See if the problem only happens when Bluetooth is enabled.
4) Remove the opportunistic roaming .plist file
5) Remove all .plist files and rebuild the connection from scratch
6) Install all intermediate dot1x certificates and set every cert
in the chain to trusted status.
7) Apply the setting that prevents changing networks without authorization.