It seems that this is bug only in some versions of AutoIt.
3.2.12.1 - OK
3.3.12.0 - BUG
3.3.13.14 - OK
There is simple workaround:
...
$frmmain = GUICreate("DM MyRadio", 407, 411, -1, -1)
$MenuItem1 = GUICtrlCreateMenu("MenuItem")
...
$StatusBar1 = _GUICtrlStatusBar_Create($frmmain)
GUIRegisterMsg($WM_SIZE, "WM_SIZE")
GUISetState(@SW_SHOW)
...
Func WM_SIZE($hWnd, $Msg, $wParam, $lParam)
_GuiCtrlStatusBar_Resize($StatusBar1)
Return $GUI_RUNDEFMSG
EndFunc
or this one:
...
$frmmain = GUICreate("DM MyRadio", 407, 411, -1, -1)
$MenuItem1 = GUICtrlCreateMenu("MenuItem")
...
$StatusBar1 = _GUICtrlStatusBar_Create($frmmain)
GUISetState(@SW_SHOW)
_GuiCtrlStatusBar_Resize($StatusBar1)