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In a file system with symlinks, the file system can be seen as a graph rather than a tree. The meaning of .. potentially becomes complicated in this environment.

There is a fairly substantial group of people, some of them big famous names, who think that the usual behavior (where crossing a symlink is different from entering a subdirectory) is a bug, and have made various efforts from time to time to "fix" it. One such fix can be seen in the -L and -P options to ksh's pwd.

Rob Pike implemented a neat hack for this in Plan 9. It is described in http://cm.bell-labs.com/sys/doc/lexnames.html. This project is to implement that logic for NetBSD.

Note however that there's another fairly substantial group of people, some of them also big famous names, who think that all of this is a load of dingo's kidneys, the existing behavior is correct, and changing it would be a bug. So it needs to be possible to switch the implementation on and off as per-process state.