This bug was fixed in the package gtk+3.0 - 3.18.9-1ubuntu3
--------------- gtk+3.0 (3.18.9-1ubuntu3) xenial; urgency=medium
* Merge branch from Marco Trevisan to hide buttons in headerbar apps when they are maximised under Unity, and to fix the gradient to look good.
-- Iain Lane <email address hidden> Thu, 24 Mar 2016 14:41:52 +0000
This bug was fixed in the package gtk+3.0 - 3.18.9-1ubuntu3
---------------
gtk+3.0 (3.18.9-1ubuntu3) xenial; urgency=medium
* Merge branch from Marco Trevisan to hide buttons in headerbar apps when
they are maximised under Unity, and to fix the gradient to look good.
-- Iain Lane <email address hidden> Thu, 24 Mar 2016 14:41:52 +0000