There is currently an issue when using two Juce based different plugin in the same host application at the same time.
As you install event handler on the application, you need to compute a different kJUCEClass for each difference instance, otherwise there is some trouble and in certain host only the newly created received drawing event (don’t ask me why).
The following code
kJUCEClass ^= t.lo;
should then happen all the time and not only when using cocoa.