I agree. If I needed to enter a CAPTCHA everywhere just to use a site I was logged into, I'd quit in a heartbeat. After the user is authenticated and logged in, there shouldn't be any more challenge requests.
But if you really want to keep this setup, then like Alex said, your changes are being overwritten by the upgrade patches. You should check the patch first to make sure it doesn't overwrite a file you've modified, and if so, re-apply the changes. But in this case, I would recommend against this kind of mod. It's very hostile to the user.
Dolphin supports requiring manual approval of new members. So if you want to make sure a user is legitimate, you can check their profile first before they're activated and able to post.
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