If rails, redstone repeaters or redstone comparators find themselves in a position they cannot naturally be placed in, and receive a block update, they will break. According to the comments in MC-129127, this should not be the case, and the block should remain a block and not break.
Steps to Reproduce:
Set a comparator in the air:
/setblock ~ ~4 ~ minecraft:comparator
Place any block next to the comparator, updating it
Linked issues
relates to
Attachments
Comments
Actually, since 1.13 the "support" block has to change for every block, in order for it to check if it's in a valid position; this is also the case for fence/pane/wall connections.
Can confirm in 20w51a.
Placing the block above them causing them to break is a bug, but placing blocks next to them should still cause them to break, since it makes contact with the placed block on the sides and should thus update them.