这是when引导时间状语从句的问题.主句和从句所用时态必须根据语义来确定.
例：I was having dinner at a restaurant when Tony Steele came in.
When she came in,I stopped eating.had done sth when...这个不用过去完成时？如果语义需要用过去完成时就用，例如：I had nearly reached the town, when the young man suddenly said, very slowly, 'Do you speak English?' （新概念第二册第14课）