As stated, Howard the Duck applies a permanent armor instead of the Iso-Loader passive for Iron Man Infinity War after the special 1.


As you can see in these screen caps, the armor passives have no timers and are a result of Howard's special one. When IMIW was below 15% health and his passives expired, the Howard placed armors behaved as the Molecular Armors, therefore it is not a visual bug.