Framing affects how students interpret, approach, and accomplish tasks. Little is known, however, about how students frame tasks in physics labs. During the first lab of a sequence designed to teach students about modeling and critical thinking with data, students test a simple model of a pendulum that breaks down with improved measurements. Using in-lab video and follow-up interviews, we identified students' frequent use of a model-verifying frame that substantially interferes with the instructional goals. We present a case study analysis of two students who approach the lab with a model-verifying frame, engage in problematic behaviors including questionable research practices, but later shift their frames to accommodate goals aligned with instructional intention. As instructors transition their instructional labs to open-inquiry experiences, an activity that directly challenges the model-verifying frame may be productive for shifting students away from this problematic frame to one that supports their engagement in authentic experimentation.