I think this would only count as an 'exploit/bug' IF forests could be regrown. Yes you may get a settler whilst getting growth but-consider this-is that necessarily a GOOD thing? Firstly, growth in city size contributes towards unhappiness and unhealthiness, which is why I am sometimes GLAD to halt growth for a while as I build my settler/worker. This is especially true if you found yourself without luxuries, different food sources and/or poor terrain (jungles nearby).
Secondly, given that you can no longer swap hammers to a new wonder if you miss out on an earlier one, I think you are better off saving your forests not for settler building, but for wonder production-or to save it against a future day when you will need to sustain a later game population. As has been stated, this really makes the forest-chop issue more of a situational thing, at least IMO.
Yours,
Aussie_Lurker.