I worked road for a year in '05, a couple of times when there was too much muck we were made to go over drains, mark, and then come back and cut them back out. Tarmac is viscoelastic, (i think thats the term?) which means when it's hot it is soft, it's heated before it's poured. It's an expensive process, a few councils I presume would not allow road crews to hold back a few gallons in the drum as it would eventually cool and could cause potential damage, saying that I don't know how those drums work, if they are heated or not. But that's likely what happened here, you have to spread and rake this stuff by hand, but even then, mistakes do happen, this drain will still drain, and it has clearly been marked for cutting. Not really any issue here