It is entirely possible that this is a combination of several effects - one or more sticky brake calipers (or clogged brake hoses), plus the effects of deceleration fuel shut-off (which sometimes is only implemented above certain rpms, and with modern systems they may even factor in driving style and previous load... so it may not always appear consistent to the driver).
I would surely have a very good look at the brake calipers and at the brake hoses.
Sometimes, when brake calipers get stuck, they become stuck intermittently.
A slightly stuck brake saddle might not even be noticeable while driving, but you should surely be able to feel it by the temperature. Get the car to out-of-town-speed, drive a few km at a constant speed, then gently pull over, stop and check the rims with the back of your hand. A really stuck brake will make the rim hot enough that you can burn yourself - and a burn inside the palms makes the hand useless, as you can't grip anything, while a burn on the back is only a bit annoying.
If you have a seizing brake caliper, don't ignore it. Not only will it eat through brakes, or even affect braking performance an handling in an emergency maneuver, the heat generated by the constant rubbing will also drastically shorten the life of the wheel bearing.
In 20 years of driving cheap, old cars, I've made it a habit to check rims and tyres at every stop. You can also detect a slow air leak on a tyre this way - the tyre losing air will be warmer than the others. (You have to keep in mind the influence of sun and weight distribution. If you were driving 100km with the summer sun to the right side of your vehicle, of course the right side tyres will be warmer than their counterparts on the other side. And in a FWD car, front right in this situation will be warmer than every other tyre. Now if front right was hot and all the other tyres were lukewarm, that would still mean something. Or if front left or rear left were the warmest... that would definitely be worth a closer look.)