@oBFusCATed :
Could you please test the attached patch (if possible) ?
It moves an improved version of your gtk-notebook stuff into notebookstyles.{cpp|h} and should also fix the issue that some of the notebooks do not use the correct TabArtProvider after a start of C::B.
Improvements to the gtk-notebook stuff:
Always use the close-icon provided by gtk (switching theme now also switches close-icon),
use the foreground-color provided by gtk for active and inactive tabs,
use different height for active tabs (as gtk does it),
use a focus rectangle as gtk does it.
On some themes the "Build messages" tab might be one (or two) pixels too large (height), because the used icon has the wrong size.
If the patch will be committed, I also commit a fixed icon.
If there aren't any objections, I will commit this patch (using gtk as TabArtProvider for auinotebooks if default tab-theme is used on wxGTK systems).
This needs gtk-2.0 as build-dependency on linux.
EDIT:
I just updated the patch to fix an issue with the focus-rectangle on the rightmost tab.
If the tab is clipped, but still has the focus, the focus-rectangle was partially drawn