The paper presents the results of an empirical study on users' behaviors when they were asked to perform a task and its variant in a usability test. Specific focus was set on assessing the users' rationality and adaptivity. The system tested was a multilingual e-Learning platform. 7 German and 3 Slovenian users were employed. Video-recordings of the two isomorphic tasks were segmented and coded. Results show that the users were rational and adaptive. KEYWORDS Mental models, situated cognition, task variant, e-learning platform