My latest painted project, the white speaks were sprayed by a friend with what he called "catalysed Acrylic" from Sherwin-Williams. I wasn't there when the work was done but did notice the primer coat was beige. He said "that was what was in the gun". I'll ask him if it was a sealer or just the paint thinned.
Other times I have brushed, rolled and sponged MDF never had the soak up problems but I was putting on very thick coats and then sponging a texture.
Let you know what the painter says as soon as I see him.