Invisible border of input-group in inverse navbar

[fredgate]

When in a inverse navbar I add a input-group containing a input and an add-on, the border of the input is badly rendered while the border of the add-on is ok. If the navbar is not inverse, all is fine.
Here is a jsfiddle showing the problem : https://jsfiddle.net/mw7ts10m/

The problem is with version alpha 5 (tested on firefox and IE11).

With the alpha 2 version, the borders was well rendered, as showed in this jsfiddle : https://jsfiddle.net/mw7ts10m/2/
It seems broken since alpha 3.

[abvalentine]

The reason is moving to a translucent border color in commit c3e4cbd
This commit also affects .custom-select and .input-group-addon.

[abvalentine]

The commit was a fix for #19136. Maybe we should make semi-transparent a border of add-on.

[fredgate]

Here is the previous rendering with version aplha 2 :

[fredgate]

I tried to add background-clip: padding-box; to input-group-addon.
At first glance, it was not too bad, although the separator between the addon and the input is not very pretty. But there is another problem. When the input receives the focus, the blue border that it gains produces the inverse effect : the input seems higher than the addon.

Here is a screenshot showing the problem :

[tillkruss]

Seeing the same issue.