Described in this KB:
At the same time a cumulative pathc for LYNC Server core components has been released with a long list of minor fixes and stability improvements.
To install the patches download and run the Cumulative Server update installer.
Remember to follow the instructions and do a stop-cswindowsservice before running the installer.
The Cumulative installer is found here:
The version number of this update is 5.0.8308.945. and it replaces the December cumulative update