Do the other sensor values work after S3, only the fan is problematic?
Nevertheless, if you say that this started occuring after a BIOS upgrade and that all other tools behave the same including Intel Control Center, then I guess this is a BIOS/Intel issue. Hard to say what exactly might be causing it, it would require a deep analysis.
I suggest that you clearly describe to Intel that even their Control Center is affected and that it occured after a BIOS upgrade.. Their 1st tier support often tries to quickly get rid of issues (mostly by referring to some FAQs, features, etc..), but if you describe precisely and insist on that, they will pass it to higher level (I know what I'm talking about

).