Certain blocks cannot be placed on or attached to a Jack o'Lantern but can be placed on pumpkin

Could be intended, see this comment by @unknown, but it is inconsistent with pumpkins which can be confusing.

Inconsistencies. One CAN place a repeater on a lit_pumpkin though not on glowstone or sea lanterns. One can place redstone wire on a staircase of glowstone which will limit the direction of signal only upwards (diode) yet when on a lit_pumpkin redstone signal is bidirectional. This is confusing since a pumpkin does not inherit these properties, yet crafting it to a jack o'lantern does. This behavior can break many designs that use lit_pumpkins as both light sources and attachable blocks (ie: redstone).

Talking it through we have decided to keep the 1.11 implementation so pumpkins and jack'o'lanterns behave the same. So Lever, Redstone Torch, Button (stone_button), Tripwire Hook, Button (wooden_button), Torch and Ladder can be placed on jack'o'lantern again.

In release version 1.12 one still cannot place torches or redstone torches on top of a Jack o'Lantern. Create new bug report or update this status? Thank you for the fix by the way.

This bug still exists in 1.12.2.

By the way, thank you for deciding to allow jack o lanterns to have stuff attached to them. I wish we could attach things to sea-lanterns and glowstone too, but having at least one block that emits light that can be used as a redstone supporting block is much appreciated. In the meantime, the sudden change from 1.11 to 1.12 has broken many of my redstone contraptions.