The bug

Models that have "uvlock" in blockstates set to true will ignore the "rotation" parameter (in models themselves) and therefore stretch the texture.
For example, if you add "rotation" to any element of the fence_side model, the texture won't rotate or will stretch (depending on the side the texture is on). But if you then set "uvlock" in the fence blockstates to false, everything works as it should.

Steps to reproduce

Install the test resource pack attached to this issue. I've used the default fence_side.json model, because it has uvlock set to true by default, and only added the "rotation": 90 tag to the uv.

Expected: texture would rotate and stretch to fit the side of an element.

Result: nothing changes. 

I've also done the same with the fence_post.json model to demonstrate that everything works as expected with it.