I'm pretty sure this is a well-known problem in general on Linux -- file locking is almost never a good solution. It sucks, since there are definitely times where it would be useful.
In any event, this is probably a low priority for glibc/kernel devs -- the fact that syncing doesn't actually behave as expected is much more important (https://lwn.net/Articles/752063/).
In any event, this is probably a low priority for glibc/kernel devs -- the fact that syncing doesn't actually behave as expected is much more important (https://lwn.net/Articles/752063/).