Meet up stay together feature rider surge bug?

I recently created a meet up with a friend for a ride around Yorkshire using the stay together function.

Several times during various stages of the ride my friend, who was behind me and pedalling less w/kg, surged way ahead and was out of site by over a minute within a very short time. There was no way I could keep up even though I was putting out higher w/kg.

Is this a bug or what is the reason for this? Are there any fixes?