The hotbar doesn't work most of the time

When ever I touch a block on the hotbar, it doesn't switch my block for that block, but instead, places the block in the area where the hot bar shows. Sometimes it does switch out my block, but other times it ignores the hotbar, the same thing happens when I try to go into the item menu. I've seen other people get this same problem resolved, but even after multiple updates, this bug still happens to all my Minecraft worlds. I don't know what to do and it's greatly annoying me. Please help.