[Modal] "blurring: true" breaks fixed content

[brownsugar]

Steps

1. Open the modal with option "blurring: true".
2. Close the modal.
3. All "position: fixed" contents are now broken.

Expected Result

The fixed content should restore fixed state when modal closed.

Actual Result

A weird situation happened.

Version

2.3.1 & 2.3.3

Testcase

Tested in Chrome 68 and Firefox 61, only modal with blurring option cause this bug.

1. This is official document page with the bug happened.
   https://semantic-ui.com/modules/modal.html#dimmer-variations
   

2. Another case of my site, the nav bar move to weird position, it should be fixed to top.
   

[jlukic]

Using filter will modify the behavior of fixed content, because filter creates a new stacking context.

I've modified modal to remove blurring after hiding modal, however, layout may change while modal is visible.