Ask HN: Whose job is it? Tester or Developer?

I work as a developer at a large consulting firm. On my small team, we have 4 developers and 3 functional people (essentially 2 testers). Often we, the developers, will get emails from one of the testers saying something along the lines of

"I logged a new defect. It's occurring in this environment... but not always. Will you take a look?" These sort of messages drive me crazy.

Should the tester be the one responsible for directly pinpointing the error? Or am I just out of line in thinking this? I do sometimes like to live in a dream world.