When the first post in a thread is placed into the moderation queue, it's actually stored in the queue as the content type being the 'thread' (not the 'post'). This will result in a report count always being 0 since reported posts are stored with the content type being 'post'.
I'm confused as to what you're reporting. What do you mean by "report count" in the context of the moderation queue? Moderating the first post is moderating the thread, so the behavior is correct (and there would be a moderation queue handler for threads).