Emily the experiment was fascinating - native speakers of English split words pretty arbitrarily, native speakers of French always split words the same way. The researcher running this experiment (she explained afterwards) was interested in people brought up bilingual from birth (I was one of her monolingual controls).
Turns out one language dominates. So if French is your dominant language, even if you speak English as a native due to being bilingual, you will consistently split words the same way every time while a monolingual English speaker will vary, arbitrarily.