Reusing yeast affect on taste

[BeerCat]

I have been wondering exactly what flavour and how much is imparted by reusing yeast? I am lazy and have been throwing a lot of my brews onto old yeast. It saves time and seems to work fast. I am sitting here drinking a Dry Irish Stout which i threw onto a St Peters Honey Porter yeast and fairly sure i can detect a very faint taste of the Porter. Although seems unlikely it could of transferred any Honey taste to my beer i still seem to taste it. I didn't at first as i drank some before it was fully conditioned. Normally i never notice as i throw a Pale Ale onto a Pale Ale etc.