The static variable is the problem, independent of any interaction or incompatibility with the other form of Fl::awake(). Since there is only one static variable callling Fl::thread_message() later in user code can only retrieve the last value assigned to this variable. Hence Fl::awake(void* message) is IMHO always unreliable unless you know that messages are queued infrequently, i.e. less than can be handled by events. A user moving the mouse permanently would likely lead to an "event overflow" dropping messages, whereas Fl::awake(F, message) queues all messages so no message can ever be lost.