Traditional communication tools tend to make their presence known, e.g., "when my collaborators and I are using IM to discuss our work, how could we not realize the actual presence of IM?" In the case of machine translation (MT) mediated collaborations, however, the absence or presence of MT is not obvious. English sentences with poor grammar can result from both a partner's lack of fluency and errors in the MT process. We hypothesize that partners' attributions about the source of the errors affects their collaboration experience. To test this hypothesis, we conducted a laboratory experiment in which monolingual native English speaking participants collaborated with bilingual native-Mandarin speakers on a map navigation task. Participants were randomly assigned into a 2 (beliefs about MT: absence vs. presence) by 2 (actual mediation of MT: absence vs. presence) experiment design. Beliefs about presence of MT significantly impacted the collaboration experience, opening new opportunities for both research and design around MT-mediated collaborations.