This had been triggered by a slew of international complaints: Children from developing countries (many of which had been liberated from themselves by the benevolent British Empire) were terrified and offended by the book's pale-skinned, blonde protagonist. He reminded them of days under British and European rule and the suffering (or 'learning' as the government preferred) that they had endured.
Historically, white people had always been unfairly picked on for trying to help the world be more like them and Jesus, so this was another major blow.
A legal battle over the book ensued, and when it was finally reprinted stringent efforts were made to completely remove any contentious material regarding race, colour and even gender. In the updated 1979 edition Sam was reimagined as a completely transparent flatworm which changed gender at will.
However, sales plummeted and, before long, environmentalists were reporting that crimes against flatworms had risen by as much as 23%.