They have different personalities, but Maddie and Mew are in full agreement when it comes to sheep
The Girls have attained the great age of five months and the honeymoon's over, so far as playing in the field is concerned.
When the dogs move out into the field the sheep (generally) retreat to a far corner, where they can watch the proceedings without attracting undue attention. Until now.
The sheep still head for their corner, but Mew and Maddie know exactly where they are, and undue attention is precisely what they have in mind.
Luckily, both puppies will come back when we call them. It isn't a problem if we're vigilant, but we're only fallible humans, and Mew and Maddie are experts at recognising and exploiting an opportunity.
Of course, when this happens there's no point in getting cross (it's our fault, after all). We have to welcome the girls back and let them know how pleased we are, while making a mental note to pay more attention in future.
In everyone's defence, however, I don't think that we, or they, are entirely to blame.
If a Chihuahua shouts: "Last one to the sheep's a pussy cat!" it's a matter of collie honour to take him up on it!