I seldom use white watercolor. I use the white of the paper and if I need to add white highlights, I use an opaque ink, gouache, or even white gel pen. I don’t think all opaque whites are that way however. I’d write to the company and ask for a replacement if you intend to use much of it. If nothing else, this will tell you something about the customer service of the company, and whether that particular color consistently dries like that.