Being that I'm still having this issue on Ubuntu 15.10, I can only conclude that this appears to be a design philosophy at Canonical rather than a bug. Logical volumes that are not necessary for system boot and/or are not on the primary disk where the OS is installed are not made available / mounted on (re)boot!
It is much better that the system comes up rather than waiting for a user input at (re)boot.
Being that I'm still having this issue on Ubuntu 15.10, I can only conclude that this appears to be a design philosophy at Canonical rather than a bug. Logical volumes that are not necessary for system boot and/or are not on the primary disk where the OS is installed are not made available / mounted on (re)boot!
It is much better that the system comes up rather than waiting for a user input at (re)boot.
Case closed, at least for me!
ak.