<form action="" class="form-horizontal form" method="post" name="myform" id="myform">

<form action="" class="form-horizontal form" method="post" name="myform" id="myform">
                                    {$form}
                                    <div class="form-body" style="padding-bottom:0">

                                        {if in_array('username', $register.field)}
                                        <div class="form-group" id="dr_row_username">
                                            <label class="col-md-2 control-label">账号</label>
                                            <div class="col-md-9">
                                                <label><input type="text" class="form-control input-large" name="data[username]" id="dr_username"></label>
                                            </div>
                                        </div>
                                        {/if}
                                        {if in_array('email', $register.field)}
                                        <div class="form-group " id="dr_row_email">
                                            <label class="col-md-2 control-label">邮箱</label>
                                            <div class="col-md-9">
                                                <label><input type="text" class="form-control input-large" name="data[email]" id="dr_email"></label>
                                            </div>
                                        </div>
                                        {/if}
                                        {if in_array('phone', $register.field)}
                                        <div class="form-group " id="dr_row_phone">
                                            <label class="col-md-2 control-label">手机号</label>
                                            <div class="col-md-9">
                                                <label><input type="text" class="form-control input-large" name="data[phone]" id="dr_phone"></label>
                                            </div>
                                        </div>
                                        {/if}
                                        <div class="form-group " id="dr_row_password">
                                            <label class="col-md-2 control-label">密码</label>
                                            <div class="col-md-9">
                                                <label><input type="password" class="form-control input-large" name="data[password]" id="dr_password"></label>
                                            </div>
                                        </div>
                                        <div class="form-group " id="dr_row_password2">
                                            <label class="col-md-2 control-label">确认密码</label>
                                            <div class="col-md-9">
                                                <label><input type="password" class="form-control input-large" name="data[password2]" id="dr_password2"></label>
                                            </div>
                                        </div>
                                        {$myfield}
                                        {if $register.code}
                                        <div class="form-group" id="dr_row_code">
                                            <label class="col-md-2 control-label">验证码</label>
                                            <div class="col-md-9">
                                                <div class="input-group input-large">
                                                    <input class="form-control placeholder-no-fix" type="text" autocomplete="off" id="dr_code" name="code">
                                                    <div class="input-group-btn fc-code">
                                                        {dr_code(120, 35)}
                                                    </div>
                                                </div>
                                            </div>
                                        </div>
                                        {/if}
                                        {if $register.sms}
<div class="mui-input-row">
	<label>验证码</label>
	<input type="text" id="dr_sms" name="data[sms]" class="mui-input-clear mui-input" placeholder="手机验证码">
	<button class="mui-btn mui-btn-warning but-yzm" type="button" onclick="dr_ajax_url('index.php?s=member&c=api&m=register_code&id='+$('#dr_value').val())">发送验证码</button>
</div>
{/if}
                                        <div class="form-actions" style="margin-top:30px">
                                            <label class="col-md-2 control-label"></label>
                                            <div class="col-md-9" style="padding-left:5px;">
                                                <label><button type="button" class="btn red" onclick="dr_ajax_member('{dr_now_url()}', 'myform');"> 立即注册</button></label>
                                                <label class="mt-checkbox mt-checkbox-outline" style="margin-left:20px;">
                                                    <input type="checkbox" name="is_protocol" value="1" checked> 我已阅读并同意
                                                    <span></span>
                                                </label>
                                                <label>
                                                    <a href="javascript:dr_show_protocol();">《用户注册协议》</a>
                                                </label>
                                            </div>
                                        </div>
                                    </div>
                                </form>

已解决，原因是参考此帖 http://www.finebug.com/7324.html

由于原帖作者之前发布的代码截图不完整，导致功能无法使用，在我反馈后，作者帖出完整代码后，正常使用了。