Zhure said:
PHB, page 117, bullet note:
" If your entire move for the round is 5 feet (a 5-foot step), enemies do not get attacks of opportunity for you moving."
So if for some reason you take a second 5-foot step, like if you were hasted, this second 5-foot step wouldn't be a protected one because it wouldn't be "your entire move for the round."
Technically, your first 5' step wouldn't be protected either, since it was not "your entire move for the round." Since it's usually not feasible to go back and redo actions in the middle of combat, I prevent players from making other moves if they have already taken a 5' step.
Take this situation:
I'm standing next to a monster, and I take a 5' step to get out of reach. I then cast
Haste on myself, and I want to move again. But since I took a 5' step already this round, I cannot move any more.
If I wanted to move away, cast
Haste, and then move again, I could do so, but I wouldn't be able to take a 5' step. I would first take a normal Move action to retreat from the monster, and draw an AoO. (It doesn't matter how far I travel.) I then cast my
Haste, and use my extra partial action for another normal Move.
In short, a Move action is different from a 5' step, and you cannot take both in the same round.