http://www.fsdeveloper.com/forum/threads/gp-and-custom-ground-lines.440977/page-2#post-780858
This is the actual statement that was quoted:
"Don't know why it didn't work for me but I deleted shaders and restarted the sim and ta-da the elevation ALT file works fine."
Kevin himself admits he does not know why it didn't work and it is reasonable to extend he does not know exactly what makes it work. One of the things he stated he did was delete shaders and another thing was restart the sim. He does not report how he discovered the "ADE_ALT" .bgl was not working, he does not say that he neglected to restart the sim after applying the "ADE_ALT" .bgl, this is a natural conclusion, given the circumstance. To make the declaration that "Kevin Firth resolved other rendering / priority issues," one is making the generous assumption that Kevin did restart the sim after applying the "ADE_ALT" .bgl. There may be any number of things he did that he did not report, the most significant thing being restarting the sim, which would apply any number of changes, the least of which rebuilding the shader cache, which is the one thing he remembered to report deleting. From that statement, one can infer
only that this procedure
might work.
Using the principal of Occam's razor, the statement that a deleted shader cache fixes elevation issues requires more than an anecdotal statement before it is considered fact and since people's attention spans are so incredibly valuable these days, one might wonder what the goal is.