Check if the window has the WS_CLIPSIBLINGS style before using the
DCX_CLIPSIBLINGS flag.

diff --git a/windows/winpos.c b/windows/winpos.c
index fc51714..79813b6 100644
--- a/windows/winpos.c
+++ b/windows/winpos.c
@@ -2595,8 +2595,12 @@
 			  != (SWP_NOMOVE | SWP_NOSIZE | SWP_NOZORDER)) )
 	{
 	    /* get a previous visible region for SWP_CopyValidBits() */
+	    DWORD flags = DCX_WINDOW;
+  
+            if (wndPtr->dwStyle & WS_CLIPSIBLINGS)
+               flags |= DCX_CLIPSIBLINGS;
 
-	    visRgn = DCE_GetVisRgn(hwnd, DCX_WINDOW | DCX_CLIPSIBLINGS, 0, 0);
+	    visRgn = DCE_GetVisRgn(hwnd, flags, 0, 0);
 	}
     }