In your other thread Enjay wrote:One thing to watch, if you place the model in a very small sector, and the model itself is quite big, you can end up with the model seeming to disappear from certain angles. The trick is to make sure that the sector where the model actor is placed is visible whenever the model should be. I sometimes do this by making a small hole sector in the middle of the 3D floor model then change the line references for that sector to be the same as the sector surrounding the model. Then I place the model in the hole and because the surrounding sector is always visible when the model is, the model never vanishes.
That's my guess as to what is happening here. As you move to the side, the sector that the model item is placed in goes out of your field of view and, as a result, the model attached to the item sitting in that sector vanishes. You have to make sure that the sector concerned is visible from any point where you can see the model if you want to avoid this problem.
This it not a new thing BTW. Doom has always done this with sprites. It's just that it tends to happen more often with models because models tend to be bigger than sprites.