I was wondering if the toppings might be the cause. I don't have the issue with non-aro blends with virginias, but also haven't smoke any straight virginias yet, nor any of the blends you mentioned PipeIT. Is propylene glycol in toppings or from the leaf? I don't use softy bits.
Propylene Glycol is a humectant (?)/ preservative used to keep the tobacco moist. It's allegedly harmless, and most people say they don't notice it in the tobacco, though personally I dislike manufacturers that use it, and certainly can notice 'something'. I can definatley smell something that smells like nail polish remover in the bowl when smoking such a blend.
I am not sure which US blends use it heavily, and which hardly use it, but some here maybe able to advise you on that, and I would say this might be a good first place to start. I think aromatics tend to use propylene glycol quite a bit, and also the 'sauce' of the aromatics can be a bit chemically from what I gather (I tend to avoid aromatics with a few exceptions, and those exceptions are hard to get in the US).
Other questions might be how much you are smoking a day, and how large the bowl is and also how you are smoking, and compare that to what you used to smoke before taking up the pipe. It could just be that you have a low nicotine tolerance, or are smoking too much. It could also be combining with other lifestyle choices.
Hope that helps. I am not an authority on any of these matters by the way, so am happy for others to correct me.
