This study examines in-service mathematics teachers' problems on linear relationships that they posed in a semi-structured problem posing situation with a group and their ideas about the factors affecting the quality of the posed problems. Eight groups of 24 teachers participated in the study. Teachers' problems, written group work, and class discussion all served as sources of data for this study. The data was mainly analyzed through qualitative methods. The results demonstrate that seven groups' problems were invalid because the problems did not meet the given conditions in the problem posing task. Their problems mostly lacked key mathematical concepts related to linear graphs, such as linearity, slopes, and y-intercepts. In class discussion, teachers dealt with the following factors that affect the quality of posed problems: misunderstanding of the problem posing situation, making inappropriate mathematical decisions, and using improper mathematical language. This study revealed that more content-focused practices are necessary to support teachers' problem posing skills.