I've noticed a little difference myself. I've always bare shaft tuned my bows. I've found that if I bareshaft tune in the heat (and humidity) of summer, I almost always have a little tweaking to do for broadheads in the fall. Or vice versa. I had perfectly tuned broadheads last fall for deer, and this spring (late may) for turkey, I noticed some eradic flight. I got out my bare shaft from last fall, and it showed much stiffer than before. And I know that it was tuned, because I did my practicing last fall with that shaft and two fletched arrows.
I think the change is more noticeable when the seasons very greatly. Here our temps are in the 70-90F range in summer with humidities 60-80%. In the fall, our temps are usually 40-70F with RH around 35-50% unless there's a weather system in the area. That's a pretty big difference in atmospheric conditions, and those are not the extremes that we experience here. It is akin to the change in arrow flight at higher altitudes.