CoreAnimation warning

In a separate thread (class which extends ThreadWithProgressWindow) i call a singleton class which should post a toast message to the Desktop. Inside the toast class a Timer runs to fade out the toast after 3 secs. Before doing that i grab a MessageManagerLock:

const MessageManagerLock mml (Thread::getCurrentThread());
ToastsController::getInstance().createToast("Skipping already imported file");

It actually works, but i get the following warning:

CoreAnimation: warning, deleted thread with uncommitted CATransaction; set CA_DEBUG_TRANSACTIONS=1 in environment to log backtraces.

Could someone please tell me what i am missing here in order to avoid that warning? Thank you!