LBC isn't showing as installed, and there is nothing on the "available for installation" tab when launching DCU through Trout's menu (only shows Trout & DCU in installed list), but everything shows fine when launching it from shortcut in Start menu.
Shouldn't it always show if it is/isn't installed no matter how it's launched?

This is by design -- the idea being that when you launch it from a program, it shows only applications and addons related to that program.

But it has been the source of much confusion and is being changed for the next version of the updater, so that the user can easily toggle between showing all items or just those related to the specific application that the Updater was triggered by.