This is confirmed on Snopes http://www.snopes.com/medical/toxins/pancake.asp
Check the expiration dates on packages like pancakes and cake mixes that have yeast which over time develop spores. Apparently, the mold that forms in old mixes can be toxic and even fatal. The mold can cause a severe allergic reaction.
Throw away ALL OUTDATED pancake mix, brownie mixes, Bisquick, cake & cookie mixes, etc., you have in your home.