I think I found a bug.
Unsatisfied with my online search on many forums regarding the matter. I have done a deep probe to the matter. But all the solutions were confusing and everyone seem to have their opinion to how that UV unwrap should work. It was clear to me the design was very strange if it's intended. It totally made no sense to how it behaved. What I have done is when ahead and download a much older version that is reputable to work properly with the least amount of issue. Version 2.66a. Afterwhich I appended all the models from 2.78b version which I created into the older clean install. And it worked as expected when I hit "Correct Aspect" during a uv unwrap operation.
And then it suddenly did not work again. I started to wonder why the behavior... and keep importing the different saves into different version of blender and then it works sometimes but other time it doesn't.
Finally, the issue was strange as it dawn on me ... when I turn on "Cycles Render" the UV unwrap operation does not work as expected! But when I switch back to the default "blender render" it worked again!
Clearly, this behavior is not intended as the UV unwrap tool is not working the same way in the 2 different rendering mode. The issue have existed since 2.66a till 2.78b.
We should report this bug.
I have created a bug report here. https://developer.blender.org/T50987 If anyone has the time to do the probe on your system, please confirm so that we know it's a consistent behavior over all machines and operating system so that we can update the bug report as need be. Thanks.
Steps to reproduce this Bug.
(Do these in Default "Blender Render" Mode or "Blender Game" Mode)
- First Unwrap a simple box in a standard 2 by 2 default uv editor setup.
- Create a new 3 by 2 texture map file.
- The uv stretches in the uv editor accordingly with the newly created rectangular uvmap. (This is not the bug, it behaves as design)
Now reapply Unwrap with "Correct Aspect" turned on, uv is corrected and behave as expected. UV map readjust itself to it now scale to the model's aspect ratio.
Do those same 1-4 steps in "Cycle render" mode.
- You will discover that uv unwrap does not react with "correct aspect" turn on or off.
- It's as if "correct aspect" stops functioning in "Cycle render" mode.