Having some issues with mSpectralDynamics AU not working in LogicX on OSX 10.9 Mavericks.
There are two different issues I have found.
1) put mSpectralDynamics in the FX section of an audio track. Click to go to presets... select a preset and LogicX CTD's. This problem has happened a few times but is inconsistent at the moment
2) put mSpectralDynamics in the FX section of an audio track. Setup presets. Play file... seems to work OK. Save session and exit. On reload no sound passes through mSpectralDynamics... it appears to be frozen and the Analysis section looks like this:

*edit* not sure if the dropbox image link is working for anyone else - but to describe it is just a wall of green colour.
No amount of disabling, enabling. Deleting and adding the plugin fixes the problem. In fact the only solution is to reboot the computer. Then it works again first session but the problem repeats.
Just thought i'd mention this here in case any others have had the issue... not sure if it is a Mavericks bug, a Logic bug or a Melda bug?
