During the past two years I have had three windows just crack for no reason at all. The first was a crank out above the kitchen sink which we had replaced at the local hardware store. Then last fall its twin also cracked (photo attached) and then this spring the top sash in the master bath also cracked (photos attached) for no apparent reason (noticed glass slivers on the window sill). For all three windows it has been the interior pane only, the glass has stayed within the frame and they all have exposure to the sun and humidity. Does anyone have a suggestion to why they might be cracking?