In Blender 2.78 RC2, the texture mapping seems to get distorted when enabling the experimental Adaptive Subsurf feature.
Attached is an example blend file
Here's what I did:
Launch Blender 2.78 RC2.
Enable experimental feature set.
Subdivide the default cube in edit mode 2 times.
Alt-Shift-S and set to To Sphere to 1.0 to round out the cube.
UV Unwrap the cube with spherical mapping.
Assign an image texture to the material.
Apply a subsurf modifier.
Open a Rendered preview viewport.
As soon as you check the Adaptive box in the subsurf modifier, you see the texture get kinked.
Example without adaptive:
Example with adaptive: