That is a situation they work towards never happening, by never leaving a behavior change in the wild long enough for such a situation to develop.

If you look closely at the kernel code it is easy to find two or more syscalls that have names and behaviors that are very similar, but where one is recommended above all the others.This is because the older syscall(s) were found to be flawed.

But rather than break existing software, they introduce a new syscall that fixes said flaws and leave the old one intact and recommend that in the future software use the new syscall.