Consider this the first of a two-part episode. With this snapshot (15w38a), Mojang introduced a bug that broke the test137E29 style glass item elevators. There was much wringing of hands and gnashing of teeth from the community. The following day, Mojang released a fix, so it was much ado about nothing.
I wrote about it at the time. Read there for more information, and my thoughts on how to best deal with this kind of situation. I’ll spend more time talking about it in the next video as well.