[bug report] when the cascade selector is assigned a value for the second time, the display is correct, but when you click to open the drop-down selector again, the displayed provinces, cities and counties are wrong, or the result of the first assignment.

[citystory]

Element UI version

2.14.1

OS/Browsers version

win10系统/谷歌浏览器版本 87.0.4280.88

Vue version

2.6.12

Reproduction Link

https://codepen.io/citystory/pen/MWjGMWe

Steps to reproduce

重现链接详见：http//jsrun.net/BmIKp。先点击左侧第一个按钮“赋值1”，再点击第二个按钮“赋值2”，然后再点左侧的Cascader组件，弹出的选框内的值是错误的。

What is Expected?

第二次赋值之后，点击Cascader组件，弹出的选框内的值应该跟第二次赋值的相同，跟未点击Cascader组件时显示的值相同。

What is actually happening?

第二次赋值之后，点击Cascader组件，弹出的选框内的值是错误的。

[element-bot]

Translation of this issue:

Element UI version

2.14.1

OS/Browsers version

Win10 system / Google browser version 87.0.4280.88

Vue version

2.6.12

Reproduction Link

https://codepen.io/citystory/pen/MWjGMWe

Steps to reproduce

Please refer to: http// jsrun.net/BmIKp 。 First click the first button on the left "Assignment 1", then click the second button "assignment 2", and then click the cascade component on the left. The value in the pop-up box is wrong.

What is Expected?

After the second assignment, click the cascade component, and the value in the pop-up selection box should be the same as that in the second assignment, and the same as the value displayed when the cascade component is not clicked.

What is actually happening?

After the second assignment, click the cascade component, and the value in the pop-up box is wrong.

[iamkun]

fixed