So you have "Data overview" widget, some items there. You click on some specific value and get a context menu with 4 options:
However, selecting "last hour", "last week" or "last month" will lead you to the very same place - graph, but with same period, which you selected once reviewing it last time. I mean, your choice ($_GET['period']) is ignored, you just get a graph.
Not that this is much of a bug, but it is more a little confusion. It could simply be one link instead of 3 maybe, leading you to the graph and there you would select the period of your interest.