The case of the shattering shower doors

When we moved into our current house (which is destined to become a rental property), we gutted the bathroom and put in an all new toilet, sink, tub/shower, floor, and beadboard on the walls. We also installed glass shower doors, based on the advice of one of the books we were reading as we read about the art of being landlords. The idea is to make the bathroom as resistant to water as possible. Apparently, tenants have a habit of not using, or even installing, shower curtains. Water sprays all over the floor, causing all kinds of damage. Obviously, not good. We wanted our bathroom to be beautiful and bomb-proof. So we got the shower doors. 

We bought the cheapest doors you can get from Home Depot, for a couple of reasons. First, it was the same thickness of glass on all the doors from about $100 (which we paid) up to at least $200, if memory serves (they don't list the thicknesses on the HD website). Only the trim appeared to be different, and for a rental property, we didn't figure we needed the fanciest doors in the world. Also, we knew and trusted the brand, Sterling by Kohler. I guess that shouldn't count for much...

...because we have had two of these doors shatter in the last two months. First, I came home from work for my lunch break to a pile of glass in the bathroom. The outer door had somehow shattered in the previous 4 hours. We managed to convince ourselves that one of our cats must have freaked out, jumped up, hit the door just right, and caused it to explode into a million bits of safety glass. I shop-vaced it up, and we ran out and bought another set of shower doors. The same set. We figured it was a once in a lifetime event, and we already had the frame up, and it was only $90, and then we'd have another spare in case a tenant managed to bust out a door at some point in the future. 

It was all good until last night at about 1am. Laying in bed, unable to sleep, I heard a pop, a crash, and then a continuing tinkle of ... something. Somehow I convinced myself that the cats had managed to knock over their food bin and I was hearing little bits of food bounce down the stairs. Unfortunately, not so. I eventually got up and discovered that the inner shower door had shattered. One large chunk had fallen into the tub already, creating a pretty little pile of glass beads. The rest was slowly dropping out off the frame. All cats were previously accounted for, and the dog too, so this was truly spontaneous. Plus, it was the inner door, so a creature would have had to have been inside the tub, freaked, bounced against the glass in just the right spot, and then managed to run and curl up on the end of the bed before I got up. Not likely. 

We got up early and knocked out the rest of the glass, shop-vaced it, and installed the spare door. We'll both get to work on time. But this seems odd. I checked the frame, and the top support is perfectly plumb. I'm calling the company soon, and probably Home Depot too. We both grew up with shower doors and never had them shatter. Is this simply a case of you get what you pay for? Even so, $90 should by you more than three months of use out of a shower door before it shatters, don't you think?