Steps to reproduce:
1) Create a new project or open an existing one.
2) Build the project for any platform with the 'Build' option.

After the building process is finished, a Finder window with the contents of the build opens. If this window is pressed, Unity's build settings window pops on top of it and doesn't disappear until the finder window is minimized (collapsed) to the Dock and restored. The issue doesn't appear if the same project is replacing another, so builds must be given different names each time to reproduce.