In North American English, they say "I don't like when..." just as they say "I don't like that...". These forms are never heard in other versions of English. Neither is "wrong": both forms should be accepted. The problem is that the course authors' experience is often limited to one form of English, so they may not be aware of the limited status of the form which they know. It is always a good idea to consult more widely on the accepted answers.