[Bug Report] Element UI table cannot scroll horizontally

[wwdDongDong]

Element UI version

2.15.7

OS/Browsers version

window10

Vue version

2.5.2

Reproduction Link

https://jsfiddle.net/wwdwwd/t7r9wzx8/7/

Steps to reproduce

Hello, I don't know how to use jsfiddle to run element, so I put my Vue code in it. You need to run a project with NPM install, which is a configuration of general vue2.0, and then add or remove the show summary attribute

Step 1: copy the following code from https://jsfiddle.net/wwdwwd/t7r9wzx8/7/

Step 2: press the horizontal scroll bar of the fixed operation column with the mouse in the actual page, and find that it can be pressed down and scrolled.

Step 3: add the show summary attribute to the El table tag, as shown in the following code

Step 4: go back to the page, refresh and repeat the second step. You will find that the horizontal scroll bar under the operation column cannot be pressed and dragged. Only the horizontal scroll bar beyond the operation column can be pressed and dragged

What is Expected?

I expect that after adding the show summary attribute, I can still press and hold the horizontal scroll bar under the fixed operation column to scroll horizontally

What is actually happening?

In fact, after I add the show summary attribute, I can't scroll horizontally by holding down the horizontal scroll bar under the fixed operation column

[wwdDongDong]

@lm312 大佬帮忙看看吧 操作列下面的滚动条按下去不能横向滚动呀

[wwdDongDong]

@lm312 在吗 可以看看嘛？

[wwdDongDong]

@mokwangquan 需要我怎么做？