The MultiModal Interface Language formalism (MMIL) has been selected as the High Level Semantic (HLS) formalism for annotating the French MEDIA dialogue corpus. This corpus is composed of human-machine dialogues in the domain of hotel reservation and tourist information. Utterances in dialogues have been previously annotated with a concept-value flat semantics for studying and evaluating spoken language understanding modules in dialogue systems. We are now interested in investigating the use of more complex representations to improve the understanding capability. The MMIL intermediate language is a high level semantic formalism that bears relevant linguistic information, from syntax up to discourse. This representation should increase the expressivity of the current annotation though at the expense of the annotation process complexity. In this paper we present our first attempt in defining the annotation guidelines for the HLS annotation of the MEDIA corpus and its effect on the annotation process itself, revealed by annotators' disagreements due to the different levels of hierarchy and the granularity of the features defined in MMIL.