I understand auto-dismissing off-topic flags as helpful on close, since those become obsolete.
But for custom flags that's rather annoying, since those are often used for an issue that goes beyond closing. In my case it's typically a migration or merge request.
What's particularly bad about this is, that the feedback "helpful" is non different from what happens when a moderator actually looked at the flag, and decided it was helpful. Perhaps the feedback should be "helpful (automatic)".
Update: I just found a clear example where community closure and flag acceptance happened at the same time. This has happened several times, but I don't remember which of my other flags where involved:
I flagged this question for migration 21h ago. It was closed(5 community votes, no diamond) and at the same time my flag was marked helpful. It's very unlikely that after 21h both events happen withing 1 min of each other by coincidence.