It does not follow that other organic compounds produced from formaldehyde, nor those that will break down into formaldehyde in given conditions, will necessarily have the same effects or will necessarily be toxic, true. On the same level, the simple fact that it is approved for use in human products does not necessarily mean that it is safe for use in bird products. Aflatoxin is a great example of that - the level considered safe for human consumption will kill birds quite effectively.
I can not speak for what is used in breads outside the United States. Here, they make it quite clear that the vinegar is added as a conditioner for the dough, not as a preservative. Unfortunately, the bread I currently have in the house is a brand that makes a big deal about not adding preservatives - a shorter shelf life which we pay for but at least I am not pickling myself when I eat it. I can not even speak for current bread production - I made the stupid mistake of simply passing on what I had been told in school by my ornithology and chemistry professors. I will take the time to check some of the cheap brands of bread and report back. However, formalin or not, the ornithologist I work with has assured me that the typical bread manufactured in the US is far too rich for birds to digest effectively.
Mark