Ok, upon further analysis, for some reason this is only the case when BigBox is set to launch into "all games" view (which is my preference for my particular build).
If I set BB to launch into "platforms" view, I can hit left or right on the game list and bring up the alphabetical table of contents on the bottom of the screen.
If I boot into BB in "all games" view, the table of contents IS functional, but the A-Z and the other icons are not visible. Booting into all games and manually switching to "platforms" then back to "all games" resolves the issue, I'm just not trying to do that every time I boot the machine up.
Any help appreciated, this is driving me coo coo.