Disappearing and Inconsistent Live Polls

When a student joins a group and answers a live poll, then goes back to `PollsDateActivity`, the date group containing the poll they just answered will disappear. Also, when admins create a new poll, enter that poll's date group, and exit the poll's date group, the poll's date group may disappear or display an incorrect number of polls.

从 PollsDateActivity 开始，重现报告中的两条流程：以学生身份回答一个正在进行的投票，并以管理员身份创建一个投票，然后进入并离开它所属的日期组。跟踪导航后日期组和投票数量如何刷新；完成的标准是相关组仍然可见，并显示正确的投票数量。

由索引模型根据 Issue 内容生成。