STemWIN GUI_Exec function problem

/* Init GUI */
GUI_Init();

/* Create graph through all LCD screen */
hGraph = GRAPH_CreateEx(0, 0, 320, 240, 0, WM_CF_SHOW, 0, GUI_ID_GRAPH0);

/* Set grids and border */
GRAPH_SetGridVis(hGraph, 1);
GRAPH_SetBorder(hGraph, 25, 5, 5, 5);

/* Create a curve for graph */
hData = GRAPH_DATA_YT_Create(GUI_DARKGREEN, 500, 0, 20);

/* Attach curve to graph */
GRAPH_AttachData(hGraph, hData);

/* Create scale for graph */
hScale = GRAPH_SCALE_Create(3, GUI_TA_LEFT, GRAPH_SCALE_CF_VERTICAL, 25);
/* Attach it to graph */
GRAPH_AttachScale(hGraph, hScale);

/* Update EMWIN GUI = do pending tasks */
/* This works, function returns non-zero, because it has some job to do */
/* And it is called first time in this project */
GUI_Exec();

/* Add manual data for testing if graph works */
GRAPH_DATA_YT_AddValue(hData, 100 + 60 * sin((float)2 * (float)5 * (float)3.14 * (float)15 / (float)255));
GRAPH_DATA_YT_AddValue(hData, 100 + 60 * sin((float)2 * (float)5 * (float)3.14 * (float)15 / (float)255));
GRAPH_DATA_YT_AddValue(hData, 100 + 60 * sin((float)2 * (float)5 * (float)3.14 * (float)15 / (float)255));
GRAPH_DATA_YT_AddValue(hData, 100 + 60 * sin((float)2 * (float)5 * (float)3.14 * (float)15 / (float)255));
GRAPH_DATA_YT_AddValue(hData, 100 + 60 * sin((float)2 * (float)5 * (float)3.14 * (float)15 / (float)255));
GRAPH_DATA_YT_AddValue(hData, 100 + 60 * sin((float)2 * (float)5 * (float)3.14 * (float)15 / (float)255));

/* Change layers for LTDC, show layer 2 on LCD */
TM_ILI9341_ChangeLayers();

while (1) {
    /* Here is my problem */
    /* Check for pending tasks */
    /* Here is function called second time and it does all pending jobs successfully */
    /* Writes 6 points to graph as set some lines above */
    /* But it does not return non-zero value anymore, it always returns zero value meaning no job to do anymore */
    if (GUI_Exec() > 0) {
        /* Toggle LED, confirm that GUI_Exec returns non-zero value */
        /* This never happens, LEDs are always zero */
        TM_DISCO_LedToggle(LED_ALL);

        /* Do some job if windows are updated */
        /* Copy layer 1 (EMWIN drawing layer) to user-visible layer 2 to avoid flickering when fast updating graphs */
        TM_ILI9341_Layer1To2();
    }

    /* Every 100 ms add new value to graph */
    if (TM_DELAY_Time() > 100) {
        /* Reset time */
        TM_DELAY_SetTime(0);

        /* Add new fake values to graph */
        GRAPH_DATA_YT_AddValue(hData, 100 + 60 * sin((float)2 * (float)5 * (float)3.14 * (float)15 / (float)255));
        GRAPH_DATA_YT_AddValue(hData, 100);
    }
}