By investing talent points in more than one talent of the next tier, you are able to uninvest talent points from the previous tier. With 1 point in three talents in the following tiers you're able to uninvest up to two points from a previous tiers.
In my first screenshot I initially put three points into Retribution, then three into Executioner's Aim, then one in Berserk, one in Dominating Presence and one in Momentum. I was then able to uninvest 2 points from Retribution or Executioner's Aim without it removing points from the 3rd tier.
My second screenshot shows an example with zero points in the first tier and only points in the second and third tier.
This only works when you have points in more than one talent in the next tier group. Three points into a single talent doesn't work and it will refund the points as expected when your points in previous tiers drop below that tiers requirements.