A very glitchy behavior. I really don't know how to describe it but by using screenshots.

How to reproduce:

1. Get in a world in 19w13b
2. Look at a block and notice if you look at different portions of the block, you can/cannot place blocks/mine that block.

Screenshots: As you can see, I'm looking at the same block, but one screenshot doesn't highlight the block.

Edit 1: No, there wasn't any armor stands. I would also like to add a detail of that area was blown up by TNT summoned in by command and that seems to be the affected area.

Edit 2: The bug seems to disappear after relog.