Ubuntu 14.04 has just recently started doing this to me too about a week ago, today being 2015-04-22. I keep Ubuntu upgraded on this 64bit PC (Intel i5) to the latest state nearly all the time.
I wonder if this helps:
When I turn on the power (with the BIOS is set to start the PC when power resumes) I often see my desktop for an instant before the system flips to the login screen.
If however I reboot the machine without downing the power, the auto logon works OK.
Ubuntu 14.04 has just recently started doing this to me too about a week ago, today being 2015-04-22. I keep Ubuntu upgraded on this 64bit PC (Intel i5) to the latest state nearly all the time.
I wonder if this helps:
When I turn on the power (with the BIOS is set to start the PC when power resumes) I often see my desktop for an instant before the system flips to the login screen.
If however I reboot the machine without downing the power, the auto logon works OK.
Happy to do any diagnostics as directed.