Overlooked or Forgotten 40k Rules

After NOVA and watching some other events, I wanted to put together a list of rules that are often forgotten, overlooked, or implemented incorrectly. These aren't necessarily the unclear rules that have debatable interpretations, but instead those that might have changed in a minor way across editions or are obscure enough to be overlooked.

Monstrous Creatures/Flying Monstrous Creatures and Cover:
MCs and FMCs treat cover the exact same way as other infantry. I heard numerous claims at NOVA that they were treated like vehicles for cover, which is just not true. In terrain like ruins with a set save, regardless of being obscured, they are just like other infantry and do not need to be 25% obscured.

D-Weapons and Armour/Cover Saves:
The D-Weapon rules were rewritten and no longer inherently ignore armour and cover saves except on the roll of a 6. Armour saves are usually irrelevant since most D-Weapons are AP2 or AP1, however, this is not always the case. For example, the Transcendent C’Tan’s Transliminal Slide is AP-. This means it isn’t nearly as effective at hurting tough infantry since 5/6 of the time they will either get their saves or be unharmed.

D-Weapons and Wound Pools: 
Because D-Weapons can cause multiple wounds, there is sometimes confusion as to whether they carry over from model to model. They do not. D-Weapons never roll to wound and instead have a result for each hit. Two D-Weapon hits with a 2-5 will do 2D3 wounds to up to 2 models, not 2D3 wounds to the unit. A single D-Weapon hit will not remove up to 12 single wound infantry models, it will simply mash one model very thoroughly.

Linebreaker:
This is one of those minor changes in 7th Edition. Linebreaker is now only scored if one or more model is within 12” of the opponent’s board edge. This means it is scored differently than before for Hammer and Anvil and Vanguard Strike deployment.

Vanguard Strike Table Edges:
In Vanguard Strike deployment, it has been clarified that the long board edge of each deployment zone is considered the players’ board edge, while the short edges will be counted as the sides. Essentially, with the change to Linebreaker, after deployment, Vanguard Strike is treated exactly like Dawn of War for deploying reserves, outflanking, and scoring Linebreaker.

Heroic Morale:
Heroic Morale (Double 1s) is only needed if a unit is already falling back and under 25% or lost combat that badly. A unit under 25% that is forced to make a morale check, but is not falling back, uses their normal leadership.

Flyers and Ongoing Reserves: 
Flyers in Ongoing Reserves always return to play via the controlling player’s board edge, meaning the long edge for Dawn of War and Vanguard, and the short edge for Hammer & Anvil.

Walker/Superheavy Walker Firing Arcs:
Walkers no longer pivot in the shooting phase. Walker weapons are assumed to have 45 degree firing arcs horizontally and vertically from the weapon mount itself.

This is just an initial list, as I'm sure there are some obscure rules I'm overlooking myself. What rules do you find are forgotten, overlooked, or misplayed in your games or gaming groups?