Linux bubastis 3.18.12-gentoo #1 SMP Tue Jun 16 16:26:19 EDT 2015 x86_64 Intel(R) Core(TM) i7-4800MQ CPU @ 2.70GHz GenuineIntel GNU/Linux
01:00.0 VGA compatible controller: NVIDIA Corporation GK107GLM [Quadro K1100M] (rev a1)
A set of texture nodes that include a connection from the Input > Coordinate into a Separate RGBA node provides values that copy the UV coordinates (usually 0..1). If that Separate RGBA node is wrapped in a group, the range of values coming out of the Coordinate changes to -1..1.
Changing it so that the group input is a blue dot instead of a yellow dot works around the problem.
Screenshots and a sample .blend file are at http://blender.stackexchange.com/questions/34894/grouping-texture-nodes-changes-the-coordinate-space?noredirect=1#comment56186_34894
The behavior of the nodes should not change just because they are wrapped in a group. It should remain consistent in all contexts.