Can't submit Typo3 forms when not logged in - php

Question

I have made a simple plugin with a form but it won't post when I'm not logged in.
Here is the file class.tx_gctest_pi1.php, created with Kickstarter.
require_once(PATH_tslib.'class.tslib_pibase.php');
class tx_gctest_pi1 extends tslib_pibase {
var $prefixId = 'tx_gctest_pi1'; // Same as class name
var $scriptRelPath = 'pi1/class.tx_gctest_pi1.php'; // Path to this script relative to the extension dir.
var $extKey = 'gc_test'; // The extension key.
var $pi_checkCHash = true;
function main($content, $conf) {
$this->conf = $conf;
$this->pi_setPiVarDefaults();
$this->pi_loadLL();
if($_POST) {
echo 'test';
}
$content='
<strong>This is a few paragraphs:</strong><br />
<p>This is line 1</p>
<p>This is line 2</p>
<h3>This is a form:</h3>
<form action="'.$this->pi_getPageLink($GLOBALS['TSFE']->id).'" method="POST">
<input type="text" name="'.$this->prefixId.'[input_field]" value="'.htmlspecialchars($this->piVars['input_field']).'">
<input type="submit" name="'.$this->prefixId.'[submit_button]" value="'.htmlspecialchars($this->pi_getLL('submit_button_label')).'">
</form>
<br />
<p>You can click here to '.$this->pi_linkToPage('get to this page again',$GLOBALS['TSFE']->id).'</p>
';
return $this->pi_wrapInBaseClass($content);
}
}
if (defined('TYPO3_MODE') && $TYPO3_CONF_VARS[TYPO3_MODE]['XCLASS']['ext/gc_test/pi1/class.tx_gctest_pi1.php']) {
include_once($TYPO3_CONF_VARS[TYPO3_MODE]['XCLASS']['ext/gc_test/pi1/class.tx_gctest_pi1.php']);
}
?>
This will output test when logged in and nothing when not logged in.
The page is reloaded but no post is sent

Answer 1

I think this has not much to do with logged in / logged out. TYPO3 caches content unless you tell it to not cache.
echo var_dump print_r debug are methods that directly display things through php. TYPO3 doesn't catch them. If you want to have something displayed, add it to e.g. $content and return $content at the end of main(). The return value of main() gets cached.
You can try this by clearing your cache in backend and refresh the page. echo etc is displayed. after a new reload, it is gone.
So, how to solve this? There are a few possibilities
make the page that contains your plugin uncached
make the plugin itself uncached
I would suggest you find out what you really want to do and then write your code that is is using caching.