Fixes #4145 image icon causes issues in header

RELEASE-NOTES.md

@@ -30,6 +30,7 @@
 - **Comments** - `small`, `large` and other comment sizes now default to global size variables.
 - **Dropdown** - Fixed issue where `selectOnKeydown` with `html` content would cause only non html content to display in `text` until blur
 - **Form Validation** - Fixes js error caused by revalidating inputs without validation rules #4497 #4547 **Thanks @cbxp**
+- **Header** - Using `image icon` or `image outline icon` would cause incorrect display within `ui header` due to namespace collision with `ui image` #4145
 - **Input/Dropdown** - Fixed rounding error causing vertical alignment of `dropdown`, `search`, `input` to sometimes appear off by 1 pixel #4279
 - **Segment** - Fixed `padded vertical segment` `very padded vertical segment` would receive horizontal padding #3012
 - **Visibility* - Fixes issue where reinitializing, `.visibility({ type: 'image'})` will cause it to re-animate when visibile again

src/definitions/elements/header.less

@@ -79,7 +79,7 @@
         Image
 --------------------*/
 
-.ui.header > .image,
+.ui.header > .image:not(.icon),
 .ui.header > img {
   display: inline-block;
   margin-top: @imageOffset;
@@ -87,7 +87,7 @@
   height: @imageHeight;
   vertical-align: @imageAlignment;
 }
-.ui.header > .image:only-child,
+.ui.header > .image:not(.icon):only-child,
 .ui.header > img:only-child {
   margin-right: @imageMargin;
 }