This bug has been around for a while. I thought I posted something about it a while back, but it's not in my list of posts.

When you look at the Training window, you have the four buttons for Single, Group, Squad, etc. and another four buttons for Recruit, Veteran, Elite, etc. What's happening is if you gain techs enabling some or all of these buttons, then either load a previous save or start a new game, these buttons do not reset. They remain selectable. Currently the only way to fix them is to exit the game and reopen it. Some code needs to be added to check these buttons against requisite techs with every load and to reset them when starting a new game.