Although not invalidating models it was quite annoying when 2nd edition rolled over to 3rd ed and Terminator squads could no longer equip any Terminator weapons. Separating one Terminator Squad into a shooty squad and a melee squad was a pain considering I was buying the squad one Terminator blister pack at a time with pocket money. *flashback noise*
Not being able to tool up assault squads after 3rd was a bit lame as well. I do feel sorry for the people that lost chunks of their army (or their whole army for Black Templars).