"Courteney's Cougar Town dressing room. The girl's got style," Arquette wrote on his Twitter page last Friday, adding a picture of the room.
Things seemed so normal that colleagues were shocked Monday to hear that the couple had decided to try a "trial separation" after 11 years of marriage. The couple said in a statement that the split "dates back for some time."
"There was no indication anything was going on. This news today, it's very sad," one source tells PEOPLE.
"They we're perfectly professional, though not particularly cuddly," another observer says. "[They] just talked to friends on set. None of them knew about the split until just now."
As production resumed Monday, it was "business as usual at the show," the source says.