While placing block(s) extremely close to you (such as placing glass in the wall while standing against that wall in MY case), they disappear both from the world and the inventory one by one as you place them. I've lost about 4 glass trying this a few times, and also tested it with Oak wood planks, cobblestone, and dirt. I have no way to record it because of Apple's restrictions against recording a device on-screen, so you can try it yourself if possible. It is a huge bug though, because blocking yourself in an emergency could go a bit wrong if standing too close to the block-collision radius.
Also, a picture wouldn't be able to prove anything, but if I find out HOW I can (or if you figure something out and you request me to screenshot something specific), then I will do so. Thanks!