I can't understand why that happens. If I use a modified DLL to send in the Pimax values and render the special rotated views, the trees just move around with the other objects as expected.
The trees do go through a different render system, because they are moving objects, but they are all rendered to the same render target and LFS is supposed to be in control of that. Some other objects go through that system: the driver body, the wind turbines, the marshals, the skid marks, tyres on cars, the visible frame on the MRT and the suspension parts on single seaters and LX cars, the racing line (when you press 4). Quite a lot in fact.
As I can't reproduce the problem, I need to ask you some questions:
1) I'd be interested to know if there is a problem with any of the other special objects listed above.
2) Can you post a screenshot of the problem? Please switch on the "double" option for "Monitor view" so you see both eye views on the LFS window. Then you can press CTRL+S at any time and you should find a screenshot in your data\shots folder.
I've only seen a similar thing before with some 3D glasses which were trying to hook into the D3D code to produce a 3D image from programs that weren't designed to produce 3D images. But they didn't really know what to do with anything that didn't go through the main pipeline, so all those objects I listed were not positioned correctly. But that shouldn't be happening here as LFS does the 3D views itself.