If I'm using my computer keyboard to play notes when I switch presets in a third party synth the keyboard doesn't play any notes until I click the keyboard icon in the top right corner off and then click it back on. This happened on Alchemy, Omnisphere, and Kontakt 3. I didn't try it on any other plugs but I assume it's an issue if it happens on all those.
This happened all the time in the last beta but happens sporadically on b10.
MBP OSX 10.5