NVIDIA GeForce GT 755M 1 GB
Worked: Never? spotted it about 7 years ago, but only just around to filing this!
Short description of error
Layers buttons are often lost from the 3D View's Header when exiting edit mode - when going back to object mode after editing an object, the layers toggle buttons are sometimes simply not there!
Exact steps for others to reproduce the error
Apologies, this is another bug where I do not know exactly when it happens, so is hard for me to give instructions to reproduce, but again, it has been observed for multiple years, on multiple hardwares running multiple operating systems, so I am certain that it is just a Blender 'thing' that I now simply just work around - There is a definite work around too - all you need to do is create another 3d view with the corner grabber, and you will see that this new window's header has the layers buttons! So, make this new view and kill the old view, and you're back in business.