Chain command blocks running when they shouldn't be

During my time using command blocks, it seemed as though chain command blocks would only run when the command output of something was true. In the newest snapshot they seem to be running even when the command output of something is false. This is breaking a lot of my command contraptions as any and all chain command blocks are now running when they shouldn't be. I heard that they got optimized, but I can't imagine that this is what was meant.