Zillow estimate decreases???

[Greg Sharp]

I have seen numerous Zillow estimates that have dropped 10%-20% after being listed. I am assuming the Zillow algorithm uses list price to factor its Zestimate, but I am wondering if the pre-drop price could still be used. Has anyone else seen this, or does anyone have any insight as to why these estimates might be dropping so much. The other houses in the neighborhoods are not dropping.