Alacrity Boot Rune Not Granting +20 Movespeed

Hi,

In game I was playing ADC and had Berserker's Greaves for boots. At the fountain I upgraded my greaves to the alacrity rune, and I noticed my movespeed number was exactly the same. So I clicked the undo button on the alacrity rune back to berserkers greaves without a rune. No movespeed change. Re-purchased alacrity rune, refunded, and did this a few times and my movespeed never changed. Keep in mind I ONLY tested this with Berserker's Greaves. I was playing Jinx, and had other movespeed items (phantom dancer, stattik shiv).