This study addresses the question of whether the use of problematic strategies is a threat to the effectiveness of a specific form of extensive reading. Extensive reading has been considered an effective way to receive comprehensible input in second language learning, and its benefits on the development of second language reading skills have been well documented. Meanwhile, it is also common that extensive reading is implemented as a part of existing language courses. In such courses, learners' performance on comprehension tasks could affect their course grades. A potential concern here is that problematic strategies, including cheating, are employed to increase task performance. Interview and questionnaire surveys were conducted in the English department of a Japanese university, where active efforts are made to realize principle-based extensive reading, and extensive reading performance (i.e., the amount of reading) affects students' course grades. While there were large individual and group differences in the students' behavior, the results provide evidence that the use of problematic strategies is a real threat to the effectiveness of extensive reading. Based on our observations, we also propose some possible ways of promoting positive engagement with extensive reading.