As a result, some issues arise, such as code that is stuck on GPLv2 (e.g. removed the upgrade clause like the Linux kernel) may be incompatible with LGPLv3.
This blog tries to explain some of the issues. http://nmav.gnutls.org/2013/03/the-perils-of-lgplv3.html
To make a car analogy, if the tires are made under LGPLv3, you got to tell them what kind of rubber it is made of and permit car owners to change the tire without the car saying "unapproved parts used, so I will refuse to start now until you have bought approved tires from an official car dealer". Every car made before 2000 managed to do this without even thinking about it.
FSF consider GPLv2 to be incompatible with this deal from a US-legal view, which is the same view that claim "further restrictions" only covers restrictions made from software licenses.