This is a callback to a problem from rev161, mentioned here: r161-bumpmapping_t95603
After many updates, the problem is still there. When you set either extend-box-horizontal or extend-box-vertical to any value other than 0, your shader will not work as intended. vTex.y coordinates get flipped upside down and the borders of the image in the shader seem to extend way beyond the image's actual borders.
I created two videos to illustrate this, a shader that simulates a tree bending left and right periodically, and with more intensity the farther the pixel is from the root. The only difference in the two videos, is that I changed the extend-box-horizontal in the shader from 0 to 5.
Working like it should http://youtu.be/Kzpgi4Z6YUc
NOT working http://youtu.be/ml5X0IB7Kes
Problem exists at least in the previewer, once exported, on firefox, chrome and node webkit