In this article, we present a study that tests the Interface Hypothesis (Sorace and Filiaci, 2006) at the syntax-pragmatics interface and its possible extension to the syntax-morphology interface in two groups of first language (L1) speakers of Shipibo with different levels of formal instruction in Spanish as a second language (L2). Shipibo is a mixed null subject language that only allows third person null subjects and has no person morphology on the verb. Spanish is a null subject language with rich person morphology on the verb. Evidence of acquisition of a core syntactic property (the extension of null subject licensing from third to first person subjects) was found in the speech of both groups of Shipibo speakers. No significant evidence of residual non-native patterns at the syntax-morphology interface was found (subject-verb mismatches in person) in the group with higher levels of formal instruction. At the syntax-pragmatics interface, we found non-native distribution of first person null subjects in both groups of Shipibo speakers that indicates residual transfer of discourse organization properties concerning topics from Shipibo into Spanish. (Contains 14 notes, 7 tables, and 2 figures.)