Unfortunately I think there is no solution to this problem. I had the same problem a year ago and posted it about it here.
http://www.quiltingboard.com/main-f1...p-t217781.html
The tufts were not loose but the actual pile migrating up through the top. I did a bit of on line research and came across many other LAQ who have experienced this problem and the general consensus was it is the nature of the beast, sometimes it happens, sometimes it doesn't. I have not had the patience or the courage to give Minkee a second chance, even though I love it's silky luxurious soft texture.
I too tried changing needle sizes both ways, going larger and smaller. I was quilting with a poly batting and the top fabric was not a loose weave. One thing I didn't try was changing to a more slippery thread. I was using a cotton thread and it is possible the cotton fibers were coaxing the minkee fibers up through the batting and top. Perhaps switching to a poly thread or a super fine thread like bottom line or So Fine (or even more fine silk or invisifil) will help. W&N is a dense batting and if it isn't keeping those minkee fibers from migrating through, I really don't know what will help if anything. I think some minkees just have a really high pile and others don't which may be why so many have been able to quilt with it as a backing without issue.