Scroll bar doesn't work throughout the game

Wherever there is a scroll bar in this game, it won't work. The place this causes the biggest problem is the Inventory screen. For example, the Building Blocks tab has a different color scroll bar than the Redstone tab, because there is more "Building" stuff there than the five rows that are displayed. So, the game is recognizing that it should scroll... it just doesn't. I have tried uninstalling and reinstalling Minecraft. I am very new to Minecraft... actually my kids are playing it. I have searched for two days and haven't found anything (actually one post that recommended reinstalling, which is why I tried that).