Idol of The Dreamer consider only one gem

[Magnarofgael-mirage-raceway]

Hi,
I’ve crafted the above trinket on lvl4 quality, the item description says , it should given 49 haste/Ysmerald what’s equipped, and this goes up to 18 stack, after will give 841 secondary stats split evenly.
I have on the character 5 Ysmerald gem, but for example on stack 10 still given only 490 haste instead of 5 times 490.
It looks like for me only one equipped gem considered, and all others ignored, which means not really worth in this case the trinket.
https://www.wowhead.com/item=193005/idol-of-the-dreamer