Earlier today Apple released an update to MainStage, which as the Logic Studio users will know is part of the Logic Studio. Version 2.1.3 brings a host of bug fixes and improvements to the pro tool, all of which are detailed in the release notes.
The update includes performance enhancements and fixes to issues related to MIDI processing and compatibility with third-party plug-ins and keyboards. Stability of the app under certain conditions has been improved, and a number of general issues dealing with the user interface and mappings are resolved.
MainStage 2.1.3 is available through Software Update or can be downloaded through the Logic Studio download page (requires an Apple ID).