I noticed this shortly after tanks DLC released. It's a pretty minor cosmetic change which looks quite odd due to the shadowing in the texture around the camera from when the cover was there. The cover can still be seen on the BTR-K Kamysh's commander's camera, and the Gorgon did have it in game versions before the Tanks DLC update. Replacement would be much appreciated, but I'm not sure if it was intentionally removed or an oversight.
The cover can quite clearly be seen here;
Here it is as it currently appears without the cover;
And here is the BTR-K's turret with the cover;