`rename` fails to overwrite existing files

[mwatts15]

$ touch x
$ touch y
$ mv y x
$ ls

Expected:
x
Actual:
1#x 2#x x

[mwatts15]

A little more detail: The overwrite shouldn't occur everywhere the same file (base)name is encountered in a create/rename operation. In this case:

mkdir -p a/b/c
touch a/b/c/f
touch a/b/g
mv a/b/g a/b/f

the current behavior, where the file a/b/c/f is not overwritten, is desirable. This is desirable because it guards against a very real possibility of overwriting identically named files in subdirectories when importing from hierarchical file systems, which is a common usage of TagFS for me.