Technically it was wrong but practically it was not. see: http://news.ycombinator.com/item?id=2606096

In particular: "I trust Redis-on-disk every day less." --antirez (author of redis)

which he then qualifies in the comments as some slim use-case where it makes sense to have redis persist data to disk.

In short, it's not the intended use-case and you damned well better know what you are doing.