During the train scene, Gromit is dangling from a lamp on the ceiling. Then Feathers McGraw shoots the lamp, Gromit falls onto the train, and the lamp is on his head. But as earlier seen, there is a light bulb in the lamp, so shouldn't we have seen and heard breaking glass?
When Gromit is in the Techno-Trousers and painting the ceiling of the spare room (upside down), Wallace backs out into the upstairs hallway and bumps into Feathers. Feathers is not there until Wallace bumps into where he is supposed to be standing.
When Wallace is being dressed by the machine in the morning, it puts his sleeves on first, then his shirt and cardigan combination. When Gromit is sitting in the seat later, the machine puts on the shirt and cardigan first and the sleeves afterwards.
The close-up on the box of spare track segments that Gromit picks up shows that all the segments must be straight. However, Gromit uses these segments to guide the train round a 180 degree curve and to slalom round the legs of the table and chairs. Watching frame by frame, Gromit pulls each time a short straight segment out of the box, but it ends up much longer (and curved when necessary) when put down. The box also doesn't seem to be getting emptier.
When Gromit is getting ready to go into the bathroom in the morning, Wallace passes him fully-clothed and says, "Lovely morning, Gromit." The next shot shows Wallace back in his bathrobe blow-drying his bald head.
When the robot claw on the end of the long metal rope emerges from the motorcycle helmet on Wallace's head, it is clear that it is far too large and there is far too much metal rope to fit inside the helmet together with his head.
During the train chase Gromit and Wallace cross McGraw's way Gromit puts a segment over the existing track. It's clear when the carriages between Gromit and Wallace pass that the new track is on top of the old one rather than a cross-track piece. After Wallace snatches the locomotive, McGraw left on a little platform on 4 wheels goes smoothly over the new crossing rather than "tripping" over the crossing rails on top of his track. Even after McGraw makes a turn and reveals the crossing behind for 2 frames you can see the new rails are still lying on top of his track.