The same it just upgrade , and now I am using 14.04 with the same problem
also the problem fixed with Lenovo laptops, if ubuntu was the reason it must be fix DELL laptops also
And even who are using 14.04 and updated his kernel with their security update the same will happen , because the kernel was the problem with lenovo not the version of Ubuntu
Also I was able not to talk about Ubuntu , and said that i have Bios hardware problem, but I told to take care and warning other users from using the kernel or the version of Ubuntu, and to help to find way to fix it with them , not to say to me go to them, if software can change hardware data sheet , or firmware it's your security error
Once the UEFI is corrupted, going back to 14.04 is not going to help.
Talk to Dell support. No one is stopping you.
The problem is still not fixed with the Lenovo PCs.
Research if it is possible to re-program the UEFI chip.
Again, talk to Dell.
This is not Dell technical support, even though Dell people occasionally post here.