Students' framing of an activity – their understanding of "what is it that's going on here" [1] – shapes how they act, think, and learn. Prior research suggests that framing instructional physics laboratory activities as confirming known results is problematic for learning [2, 3]. Here, we complicate those findings by presenting a case-study of students who exhibit confirmation framing as they engage in productive behavior. In this case, data that are inconsistent with the theoretical model of the lab motivate a genuine problem for the three students, who troubleshoot their apparatus and analyze their data to construct an explanation for this anomaly. We claim that their productive behavior is supported by their confirmation framing; put another way, we claim that their confirmation framing engenders their productive behavior: the students seek to explain how they could have caused this error. The case-study reported on here is part of a larger project studying student behavior in non-traditional physics labs.