With Caley Thistle trailing to the first of Kris Doolan's goals, Ross Draper was adjudged by the linesman to have touched the ball twice at a corner in the build-up to Aaron Doran netting with a header.
The effort was belatedly ruled out, as was a Richie Foran header for the hosts after the break, when the Inverness striker appeared to be fouled by the Partick keeper Scott Fox.
"I'm very disappointed that we've not won the game," Butcher said. "It was a bizarre game. We dominated for large parts, but our final pass or final touch in and around the box let us down at times.
"Ross Draper has put the ball down and taken the corner to Aaron Doran and the linesman has said it was okay.
"It seemed to be an eternity between the corner being taken to Aaron Doran scoring and then the goal being disallowed, but the linesman has then said that the ball had been touched twice."
Partick counterpart Alan Archibald praised the linesman for having the courage to change his mind at Doran's disallowed goal.
Archibald said: "The linesman has shown character to go back and make the decision and I think it's the right decision.
"There's a lot who wouldn't have given it, even though he possibly left it too long to make the decision.
"It was a fantastic result. We're delighted. It was an excellent away performance."