Things like heat can accelerate these reactions. Light, especially UV is bad for hops and even brown bottles can be affected.
My bottles are certainly subject to heat in summer.
As for my priming - I bulk prime my beers with raw sugar that is dissolved in solution, boiled and added to my bottling fermenter. If I were only bottling a few, I reckon I would still dissolve the appropriate amount in boiling water and dose each bottle with a syringe.
I would never have considered using raw sugar for priming. I would have thought that being relatively unrefined that it would give a syrup or molasses flavour.
You can prime kegs with sugar (I think the correct dose is roughly half the amount used to prime the same batch of beer being bottled but please don't take my word - check). Maybe try sugar priming a keg and seeing if you get the same 'sweet' smell and taste once fully carbonated? Would be interesting to find out is thsi creates the difference you've noticed.
Once I get my stocks built back up I will try that and let you know.