It doesn't. They get arrested on the second planet they visit (and the fourth and fifth and eighth).

Luckily Donna is with her grandparents for at least two of those trips.

What's strange though is the fact that they are making a conscious effort to get arrested less, and it doesn't seem to be working at all. Maybe they are just multi-universally hated.

Even when Chris keeps his mouth shut he still manages to insult someone or something (probably because licking the walls of this palace was liable to dissolve it).

Really, even if the species didn't exist back in their old world, any species that contained the name Sucre as part of their classification was going to have an edible castle.