This is a frequently discussed issue. Tad Gage, of P&T magazine has commented that this is the natural fermentation note of unstoved Virginias that are aged in cakes.
To me, it doesn't influence the taste of the blend, while others report that it does. I generally groom a blend prior to smoking it, which has me empty a tin or spread out a bulk, in order to do so. Sometimes, if it's wet I'll let it air overnight. Blenders prefer to ship tobacco wet, and I'd rather deal with marginal losses in weight than open a bag or tin and find dust that the tobacco was reduced to during shipping. Very often, doing this will allow this fermentation note to fade dramatically.