The "Devices > Install Guest Additions" under virtual-libre downloads an ISO for virtualbox-guest-additions which is licensed under PUEL. It is a non-free license and hence should be marked for removal from virtualbox-libre from parabola.

References:
1) https://www.virtualbox.org/wiki/VirtualBox_PUEL

2)http://libreplanet.org/wiki/List_of_software_that_does_not_respect_the_Free_System_Distribution_Guidelines#VirtualBox_OSE_Guest_Additions

3)https://www.gnu.org/help/gnu-bucks-recipients.html (Acknowledgement of the issue by the fsf for which I received a GNU buck)