lens - When focusing at max zoom, focus is lost after zooming out. Is that normal?

On my Canon kit lens, I could completely zoom in, focus on the object and then zoom out to take the picture with the object still in focus.

Now I have a Sigma 18-200mm (with a Canon 600D) and that doesn't work. After zooming out, focus is lost and I need to refocus.

Is this lens broken or is not every lens the same with focussing combined with zooming?

Answer

The lens is a varifocal lens. Basically, it's a lens that changes focus as the focal length changes and it's quite common. Parfocal lenses, ones that maintain focus on zoom change, exist but are typically more expensive as a result.

Long story short, it's normal for a large number of consumer zoom lenses.