I have not personally experienced, but I have heard of experiences from some of my friends when we were still students. Some of the them would submit research proposals for their research electives in some clinical departments. Some of them were then told that if they will not pursue the topic within a certain number of years, the research project will be given to other trainees (eg. residents, fellows). While this may be done to ensure continuity of the output, the student must always be acknowledged as a co-investigator and a co-author in the work since he/she was primarily responsible for the conceptualization of the topic. At the end, it was still the student's intellectual property.