当使用data.table进行分组时，为什么我不能在lapply中使用FUN

I encountered the following issue with data.table when aggregating, using .SD and specifying lapply with stating the FUN argument from lapply explicitely. Is this unexpected behaviour or am I just missing something. Why can I not explicitely state FUN in lapply? The following is a reproducible example.I encountered the following issue with data.tab