Alpaca Felted Mittens

Hopefully I haven't posted these before! They are mittens from Plymouth Alpaca Grande made on large needles (surprise, surprise, I can't find the pattern and don't remember what size-11, I think), so were a fast knit. The pattern is a free pattern with yarn purchase at Amazing Threads. The thing I don't like about alpaca is that is has small bumps after felting. Anyone know why and can it be prevented???