The underquilt may have been hung from the center during drying. The down most likely clumped together at the ends. I wouldn't stress too much. I would suggest running it through the wash with just water to get any excess nikwax out and drying with tennis balls like the others suggested.
Experts correct me if I'm wrong but the down used 3 years ago wasn't hydrophobic. Untreated down will compress with water and shift more than hydrophobic down. You can search youtube for video comparisons to see what happens to down when wet.
I'm new to underquilts and such but have been using down bags for many years. The dryer always does the trick.