Operating system and graphics card
Windows 7 Ultimate x64
Short description of error
When using the Min Max of the mapping node, if the texture has not alpha on boundaries, the extrapolation of the color is weird.
Exact steps for others to reproduce the error
Based on a (as simple as possible) attached .blend file with minimum amount of steps
There are 2 blend files, one with a texture where the top is alpha but not the bottom : http://www.pasteall.org/blend/37266 and the 2nd blend has the same texture but with a row of one pixel of alpha at the bottom and then, it works as expected : http://www.pasteall.org/blend/37267
Just go in Rendered mode to see differences.