Since I started painting minis I always used black primer (gw spray paint) because it would easily cover them up and also holds well on the minis. Thinking about my painting preferences made me want to switch to white primer now: As I'm not experienced in blending and highlighting I tend to work from light to dark color tones. Unfortunately this means basecoating light colors onto black primed minis first, which is very time consuming.
So I bought a gw white primer but it doesn't seem to work at all. I shake the can before using it and keep a distance of at least 25cm for the priming process but the color won't hold and tends to flow down the minis. Plus it takes 6 or 7 passes to cover everything up.

Did I get a bad can or what is the problem here?