Adaptive Cruise Control not resuming speed after reduction

[BoeingPete]

I have a 2 month old 24 plate Yaris Cross Design. I drive it once a week to London (100 mile round-trip) on the M1 and use the ACC and Lane Trace alot, but recently noticed that sometimes, after my car has slowed down because the car Infront has reduced speed, when that car then accelerates away my car only continues to decelerate until I intervene by applying the accelerator. Then it picks up, accelerating to the selected ACC speed - usually 70mph or until it has matched the speed of the car Infront. I've tried increasing and decreasing the spacing but that hasn't had any affect. Is this likely to be a fault in the system or is there something I might be missing when using ACC, given this is the first time I've ever used ACC?

[Cyker]

That's a bit concerning... I've not experienced it in my one, but mine is an older revision and I tend to manually disable the ACC if the car in front slows and then re-engage it when they pull away, as the ACC in the early revisions is very unrefined and tends to close on the car in front too closely before suddenly braking really hard.

However, I've seen posts by people in newer revisions of other models (I think the Corolla and RAV4) who have reported this same behaviour...  

Assuming the delay wasn't just the car waiting for the gap to build again, report it to your dealer and maybe Toyota UK, maybe see if there is a firmware update for this...