The ones with the glass were older hives i first built, most of them 7-8 yrs old. Also using single strength glass... Moving them around and dropping them even gently cracks the glass. I'm pretty rough on my hives. I'm not gentle. I like to see how my designs hold up with rough use. I use all plexiglass now. Crystal clear, easy to cut and its much safer to use than glass. Problem solved and they almost never break, even shipping them.