This study examines whether the second language acquisition (L2A) of syntactic properties at the interfaces is problematic for L2 learners. English verb phrase ellipsis (VPE) was tested as an interface property which involves feature interpretability. Two subtle contrasts of VPE at different grammar-internal interfaces were examined: (a) copula "be" and lexical verb ellipsis at the syntax-lexicon interface (*John is here, and Mary will too vs. John slept, and Mary will too), and (b) progressive "be" and perfective "have" stranding at the syntax-semantics interface (*John slept, and Mary was too vs. Peter saw your parents last week, but he hasn't since). Unlike (a), the contrast in (b) requires identifying (un)interpretable features on "-ing" and "-en" to recover the semantics of the elided material. Since Saudi Arabic does not license VPE, (very-)advanced English L2 speakers whose first language (L1) is Saudi Arabic were tested. The results from a bimodal timed acceptability judgment task showed they were more target-like on the contrast at the syntax-lexicon interface than they were on the syntax-semantics interface. They particularly deviated from target-like judgments on "have" stranding which requires recognizing the perfective uninterpretable feature on "-en." These results suggest selective vulnerability at grammar-internal interfaces whenever uninterpretable features are involved.