Lot's of idiomatic usages are "grammatically incorrect". You can analyse this particular one to find supposed justifications for it being in some way "grammatical", but the fact of the matter is even educated speakers commonly say things like Here's John and Mary, and Where's the scissors?
Part of what's involved here is proximity agreement (aka the proximity principle) which causes us to inflect the verb according to the first subject, even if there are others following.
I believe it's also relevant that we tend to do this more often when the subjects ("subject", with something like scissors which are grammatically plural but semantically singular) are perceived as a single thing. Thus, "the news" is effectively one thing containing some good and some bad parts. And John and Mary are being spoken of as one couple arriving, rather than two separate people.