Created attachment 338573 [details]
Test url: https://smartslider3.com/bugs/webkit/flexbox11.1/index.html
Some texts on the layout are not aligned well in Safari 11.1, but works fine in technology preview 11.2 release 54.
When I select those texts in Safari 11.1, the text starts to behave correctly, but there might be glitches.
Video demo: https://www.youtube.com/watch?v=nLSCT75jt-Y
Also Safari 11.0 affected by this bug.