Learning styles are considered as an important factor in education, however, often students have to learn from material or in courses which do not support their learning styles. A challenge in the area of adaptivity is not only to provide learners with courses that fit the students' learning styles but can also veer towards supporting students to learn in courses that does not match their learning styles. In this paper, we analyse the interactions between students' learning styles, their achievement, and their general behaviour in a course that is mismatched regarding their learning styles. The impact of the strength of learning style preferences on achievement, correlations between particular learning styles and achievement, as well as students' behaviour with respect to their achievement and their learning styles are analysed and discussed. As a result, we found that students with strong learning style preferences have more difficulties in learning in mismatched courses. Furthermore, the results show that reflective learners can cope better with mismatched courses than active learners. Moreover, we found that learners with different learning styles and achievement have different behaviour in the course as well as identified correlations between the behaviour and the achievement considering the students' learning styles. The results of this study help, on one hand, to get a better understanding of the interactions between students' learning styles, achievement, and behaviour in a mismatched course and, on the other hand, provide information about how to identify learners who might face difficulties in learning in a mismatched course.