The orange tree somehow grows without being watered.
In the UK version, adult voices can be heard along with the kids' voices in the answer to the Thinking Time segment.
When Steve spots the first clue, a part of the boots is cut off. Also, the boots disappear when Steve walks to Mr. Salt and Mrs. Pepper.
When Blue Skidoos home, her skidoo sound isn't heard, but Steve's is. This is most likely due to the music.
Blue has two barking errors in this episode: When Steve says "the mail's here", her mouth doesn't move, but her barking sound is heard. Before Blue Skidoos home, her mouth moves, but her barking sound isn't heard.
The latter of Freddy's arm can still be seen when he and Fifi walk their garden, and again before Steve and Blue Skidoo home.