If this issue is a duplicate, I'm sorry. But I was messing around with beds in the 17w16a snapshot, and I encountered a weird glitch.

When a bed is replaced with another TileEntity block (like a banner or a chest) via a command, the block still renders as a bed (and not as the block itself). It does not work the other way around (a.k.a. replacing a TileEntity with a bed). The issue does not occur if the bed is replaced with a "regular" block (like stone).

Edit: Does not work with every TileEntity, furnaces for example will still render as themselves.

Notes:
° The orientation/part of the bed depends of the metadata of the placed block (which means on the "banner" screenshot, the other banner has a metadata of 8).
° It is not preserved when saving, so quitting then reloading the world will fix this.

Instructions:
1/ Place a bed.
2/ Replace it with /setblock or /fill.
3/ The bed looks like it's still there, but it's not.