I started on minoxidil about 3 weeks ago, and started Nizoral a week ago to combat the major flaking. So far I have noticed more shedding after Nizoral use (just 2x so far). It might just be a coincidence. It could just be the minoxidil causing the shedding.
I have not read anything about Nizoral causing shedding... though by no means have I thoroughly researched it.