When Dermot and Maria visit Mrs Brown at her stall at the beginning of the film (when Dermot is wearing the gecko costume) in some shots the bunch of papers he is holding has a rubber band around them, and some there isn't.
When Buster is first seen on the horse its a black and white paint with the entire back end being black. When it cuts to show Dermot and Buster riding it thru the city, its a clearly different horse. Still a black and white paint, but with much more white and the back end is not all black.
When Mrs Brown and Winnie are in the confession box, the green screen is reflected in Mrs Brown's glasses a few times.
At the start when Mrs Brown realizes she is running late for work, she looks up at the clock to see that it is 5:15(pm). But it would clearly be in the morning as the other women running their stalls are going to work the same time as Mrs Brown.
When Dermot and Buster arrive at the court room with the receipt, Dermot is seen on the horse in a chicken costume storming in. However in the next shot, is seen sitting in the crowd with a blue shirt on waiting for the verdict.