Event segmentation tests have shown substantial overlaps in how adults recognize starts and endpoints as events unfold. However, far less is known about what role different language systems play in the process. Variations in grammatical aspect have been shown to influence event processing. We tested how closely first language (L1) speakers of Mandarin and English versus Mandarin learners of English as a second language (L2) align event boundaries with event-internal changes. We used two event boundary marking tasks (online/offline) and a sorting task. Participants saw 60 animations; their task was to indicate starts and endpoints. For punctual events (e.g., "breaking a wall"), Mandarin L1 speakers and Mandarin learners of English L2 were significantly further from event transitions than English L1 speakers. This pattern was replicated in the untimed experiment but not in sorting transitions, jointly suggesting that Mandarin L1 and Mandarin learners of English L2 may be less attentive to segmentation of phases surrounding transitions than English L1 speakers. We argue that this variation reflects L1-specific encoding of ongoingness.