FWIW, I have occasionally had pink staining on prints using Artcraft Amidol, and on a variety of papers, not just one specific brand or type. When it happens, its always on the first, second, and sometimes third print to be developed after mixing the solution. Not being a chemist, I cannot explain why this happens, nor will I try to. Once one or two prints have been developed, everything settles down and works fine.
Doesn't happen every time, just occasionally.