Many instructional physics labs are shifting to teach experimentation skills, rather than to demonstrate or confirm canonical physics phenomena. Our previous work found that many students engage in questionable research practices in attempts to confirm the canonical physics phenomena, even when confirmation is explicitly not the goal of the lab. This exploratory study aimed to answer three research questions: (RQ1) What are students' expectations about the purpose of labs when they enter introductory physics?, (RQ2) How do their prior experiences shape those expectations?, (RQ3) In what ways do those expectations relate to their engagement in questionable research practices? Through open-response surveys, we found that students overwhelmingly expressed confirmatory beliefs about the purpose of labs. Through interviews, we found that students' prior lab experiences were also overwhelmingly confirmatory, despite varying degrees of structure. We then used video of individual groups to explore the ways in which questionable research practices manifest through confirmatory expectations. We confirm previous work that students' confirmatory expectations can lead them to engage in questionable research practices, but find that these behaviors occur despite instructional messaging about an alternative purpose. Our analyses also suggest that engagement in questionable research practices is more frequent than the previous results indicated through analysis of submitted lab notes. These results further illuminate issues with traditional labs, but suggest that the confirmatory goals, perhaps more so than high structure, are problematic. © 2020 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/" Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.