At the part where Ducky is putting the light fixture back in the porch roof, look at the size of the hole and the light. You can plainly hear that the light is solid and hard. The light is too big to fit in the hole. There's no way it could have gotten back in.
You forgot about the metal base cieling lights have. The bulb would have fit perfectly through the hole that was made for the metal base on the porch. This is not a slip up.
I think that when you are talking about animation, it is very hard for things to be considered "slip-ups." If the film makers were concerned about absolute reality, they would use a different medium.
But anyway... The light definitely could not have fit though the hole. No circular object will fit though a hole cut with even a slightly smaller diameter, no matter what angle you tilt it. The base of the light in the movie was wider than the hole, because no air gaps were shown. You may be thinking "What if they are the EXACT same size?", but this level of precision is only possible in a computer world.
Another slight mistake is that when they were inside the ceiling above the light, there was no wooden beam to mount the electrical box for the light.
But I suppose the animator probably never installed a light before.
What is it with you people insulting the animators? "I guess the animator never installed a light before"???? This is a KID's movie, do you reckon a kid's gonna notice "Oh my gosh, the light won't fit in there!". How many kids do you reckon have installed a light bulb before???