A second cache miss. That the language almost (1) forces the language implementation to be inefficient doesn't give those writing programs in the language to ignore further inefficiencies.

(1) A sufficiently smart compiler could, in some cases, convert a data structure that logically uses reference types into one that uses value types in the compiled code (I think that's highly hypothetical in this case, as it almost isn't worth spending time on for compiler writers, given that it will be possible very rarely)