I was thinking it was fused to the flange after 60 years of corrosion, but you may be right. (It occurred to me after spraying the WD-40 that combining a highly flammable spray with highly flammable sewer gases may not have been the best idea.)
I don't remember exactly where I saw it. I think it was one of the eHow articles on how to remove old closet bolts. There are lots of mentions of methane being present in sewer gases and that being a risk of combustion.
Well that explains it. An eHow article. Never in my entire lifetime has that ever happened. I can see how imaginary things like that are important to some people when they start writing articles.
At least something like "Don't run with sissors!" I can see happening.
I watched a video from a plumbing supply company on how to replace a closet flange and not one of the many DIY types where they said to use a propane, etc. torch on the flange. I don't remember if this was to melt the lead chalk or burn off old wax.
I also didn't have room for the extra nuts on closet bolts.