i tried to show it here:
inside a vertical box ,
if i duplicate buttons having no child objects then everything works fine.
but problem happened whenever i attempt that with button having a text block inside it.
i did some debug.
most probably problem is in 568 line from:
Z:\UnrealEngine_4.7.2_release_Build\Engine\Source\Editor\UMGEditor\Private\WidgetBlueprintEditorUtils.cpp 's