BUG: sorter direction incorrect with web component slot

[YumiChen]

Version:0.16.45

Are you able to reproduce the bug from the demo?

• [x] Yes
• [ ] No

What is the expected behavior? Given a parent web component instance rendering some elements with slot, in the shadowDOM, if the parent element of slot got display: flex style, the sorter should be vertical, for in the result the elements are aligned horizontally.

What is the current behavior? The sorter would be horizontal.

Are you able to attach screenshots, screencasts or a live demo?

• [x] Yes (attach)
• [ ] No

https://jsfiddle.net/72dyhu6L/