**Blender Version**
Broken: 2.7x, 2.8x
**Short description of error**
The "Straighten" operator doesn't always work and isn't well documented in the manual.
**Exact steps for others to reproduce the error**
Open default file
go to the uv editor
press shift W
try to figure out what straighten does, sometimes it aligns vertices in a random direction, sometimes it does nothing.
open the manual
still have no clue.