I did a bit of trial and error on this problem. I've decided to use an old exe from last October when flying ETO2015, one which doesn't display this weird anomaly on my system. While I was trying out all these things, I realised that in terrains with a lot of T-Mods, I was getting a lot of stalling at 100% loading and also freezing in-game, most particularly when using Alt N. I was using SagginB's 512x512 terrains, so I built an alternative install of his optional 256x256 versions and this seems to have eliminated all these complications. There is very little downgrade in appearance with the change. In other words, the combination of HR textures and multiple ground-objects might put a wee bit of excessive strain on game memory, or something like that.