After an active gadget deactivates, Intuition sends it a GM_GOINACTIVE
message (defined in <intuition/gadgetclass.h>):

    struct gpGoInactive
    {
        ULONG             MethodID;    /* GM_GOINACTIVE */
        struct GadgetInfo *gpgi_GInfo;

        /* V37 field only!  DO NOT attempt to read under V36!          */
        ULONG             gpgi_Abort; /* gpgi_Abort=1 if gadget was    */
                                      /* aborted by Intuition          */
                                      /* and 0 if gadget went inactive */
                                      /* at its own request.           */
    };

The gpgi_Abort field contains either a 0 or 1.  If 0, the gadget became
inactive on its own power (because the gm_goactive or gm_handleinput
method returned something besides gmr_meactive).  if gpgi_abort is 1,
Intuition aborted this active gadget.  Some instances where Intuition
aborts a gadget include: the user clicked in another window or screen, an
application removed the active gadget with RemoveGList(),  and an
application called activewindow() on a window other than the gadget's
window.