I know that the option "Long term support releases only" for the "Software Sources/Updates/Show new distribution releases" GUI allows an upgrade between Long Term Support releases (community docs).
Moreover, in "/etc/update-manager/release-upgrades" can be read:
Note that this option should not be used if the currently-running release is not itself an LTS release, since in that case the upgrader won't be able to determine if a newer release is available.
From what I understand that if I select this option in 13.10 I won't be advertised about the incoming 14.04 LTS release. I cannot understand the reasoning behind this behavior or the limitation implied by the "won't be able" above.
Besides, shouldn't that be advised also in the GUI?
Thanks for your responses.