This paper investigates whether there is a correlation between the development of agreement and the unlearning of null subjects and also how the null subjects of Korean EFL learners’ interlanguage are represented in topic-bound positions. The results of this study show that the unlearning of null subjects does not necessarily help the development of the third person singular morpheme like previously put forth by pro-drop analysis, which disconfirms the long-lived belief, MUH (Morphological Uniformity Hypothesis). On the contrary, the results also show that the positions of null arguments actually conform to the positions of topic-bound positions, which leads to the suggestion of the topic-drop analysis of null subjects.