Junior design professionals experience conflicts in collaboration with others, with value differences being one of the issues influencing such conflicts. In a retrospective interview study with 22 design professionals, we collected 32 cases of perceived conflicts. We used a grounded theory approach to analyse these cases, resulting in five conflict categories that group 24 distinct value differences arising in 10 critical moments, an event that causes the value-based conflict. Thus, value differences are underlying the perceived conflicts of junior design professionals on many different occasions during collaboration with others. Conclusions are drawn on setting up guidelines for addressing values in co-design practices and supporting junior designers in their professional development.