Just open the attached blend and press G to move the vertex in the UV window; pet is activated but it works only in the space starting from the left corner of the image space to the right, and that's because, in the Mesh Tool panel on the left, X Mirror is selected. Deselecting X Mirror re-establish the normal behaviour.
I don't think this is a new feature, so I thought to report.

Blender25_r38682 under Ubuntu 10.04 64 bit.