http://forum.zdoom.org/potato.php?t=8457
For some reason, GZDoom handles the holographic device differently than ZDoom.There obviously is a holographic device that shows the "cloaked guy". The object is obviously is very small and on the ground. That's clear.
However, there is a problem..
In Strife, if you are generally at the same floor level as the device, you "bump into it" like any solid object.
In GZDoom, the hologram (as an extension of the holographic device) is considered a solid object. So when you shoot the hologram, you hit the device. There's supposed to be a separation of the device as a small solid object and the hologram which cannot be hit.
Also:
The only time you can "go through" the image is when you jump over the device or use the higher level (the same height the carpet is on) and "run" over the image/device.