This week I upgraded from 2011 to 2014 and have noticed a major change in rotating the UCS around only the Z-axis.
Looking at the attached image (the blue box is just to represent the relationship between the pipes):
I want to, as a simple example, rotate the UCS around the Z-axis from the end of one pipe to the end of the other.
In 2011 UCS, Z would allow me to select the end of one pipe and the end of the other and rotate to the angle of the red line shown.
In 2014 UCS, Z rotates the UCS from some unrelated point.
In 2014 UCS then selecting the two ends rotates the UCS X-axis to the direct line between the two.
In a working scenario the end of the two pipes would be in vastly different positions. Drawing a line between them, flattening it then using UCS, E on the flattened line give the functionality I want, but is a very slow way of doing it.
I have been researching this for about 3 hours and I can't find an actual answer other than "that's just the way it is now". Surely not.
I did find this thread which seems to suggest there is no way of selecting 2 points for a Z-axis rotation.
TL;DR
In 2011 if I wanted to rotate the UCS around the Z-axis I would type UCS, Z then select 2 points and the UCS would rotate around the Z-axis but the X & Y axis would remain as it was. This is no longer the case in 2014, how do I do this now?