Zend_Validate_File_Upload may throw E_Notice warnings during validation.

public function isValid($value, $file = null)
{
    $this->_messages = null;
    if (array_key_exists($value, $this->_files)) {
        $files[$value] = $this->_files[$value];
    } else {
        foreach ($this->_files as $file => $content) {
            if (isset($content['name']) && ($content['name'] === $value)) {
                $files[$file] = $this->_files[$file];
            }

            if (isset($content['tmp_name']) && ($content['tmp_name'] === $value)) {
                $files[$file] = $this->_files[$file];
            }
        }
    }

Should be

public function isValid($value, $file = null)
{
    $this->_messages = null;

if (is_array($this->_files) && array_key_exists($value, $this->_files)) { $files[$value] = $this->_files[$value]; } else { foreach ($this->_files as $file => $content) { if (isset($content['name']) && ($content['name'] === $value)) { $files[$file] = $this->_files[$file]; }

            if (isset($content['tmp_name']) && ($content['tmp_name'] === $value)) {
                $files[$file] = $this->_files[$file];
            }
        }
    }