He was all smiles when Jason Shackell's opened the scoring for the away side, but his frown was turned upside down five minutes into injury time when Dunn lashed home with his left foot.
Dyche was not at all happy when the goal went in, he and his team were ready to celebrate their first victory over Rovers for 34 years, until Dunn spoilt his plans.
So he played the offside card, he said: "It doesn't feel like a defeat, not at all. It feels like a result that's been taken away from us by an official's decision.
"We've had too many of them. I've seen it and David's two yards offside.
"That is the turning point in a game we deserved three points in and, of course, the bragging rights.
"The offside goal at that stage of the game is unacceptable, I think."
It's believed that Rovers have set up a tissue fund in the main reception at Ewood Park.