Reduntant leading ../ is added to sprite url

[rmrfhome]

I run a task with such config
{ cssFile: "sprite.css", svg: { sprite: "sprite.svg" } }
and expect to have such sprite url in the css file
background-image: url("sprite.svg");
but i get this one invalid (in fact, the css and the sprite file are generated into same directory)
background-image: url("../sprite.svg");