Within online communities, social norms that both set expectations for and regulate behavior can be vital to the overall welfare of the community–particularly in the context of the privacy and safety of its members. For communities where the cost of regulatory failure can be high, it is important to understand both the conditions under which norms might be effective, and when they might fail. As a case study, we consider transformative fandom, a creative community dedicated to reimagining existing media in often subversive ways. In part due to the marginalized status of many members, there are strong, longstanding norms to protect the community. Through an interview study with 25 fandom participants, we investigate social norms that have been largely effective over time at maintaining member privacy and safety, but also break down under certain circumstances. Catalysts for these breakdowns include tensions between sub-communities and an increasing presence of outsiders, though most prominently, we identify a disconnect between the norms the community needs to support and the design of the platforms they occupy.