Here is a simple fix:
In file ‘admin/view/template/setting/setting.tpl’ replace the line:
<textarea name="config_mail_alert_email" rows="5" placeholder="<?php echo $entry_mail_alert_email; ?>" id="input-alert-email" class="form-control"><?php echo $config_alert_email; ?></textarea>with this one:
<textarea name="config_alert_email" rows="5" placeholder="<?php echo $entry_mail_alert_email; ?>" id="input-alert-email" class="form-control"><?php echo $config_alert_email; ?></textarea>