`pwd -P` with systemd-homed causes inconsistent cwd state

[Kyle Laker <kyle@laker.email>]

I have found a strange behavior with ZSH when working with 
systemd-homed. After running `pwd -P` within my home directory, it seems 
as if the current working directory effectively changes to `/`. I am 
currently using ZSH 5.9 and systemd 254.

systemd-homed is configured using a BTRFS subvolume. My home directory 
is `/home/kyle` whereas the systemd-homed image is located at 
`/home/kyle.homedir`. Running `pwd -P` prints the current directory 
under the homed image path which isn't entirely unexpected (though this 
behavior differs from that of other shells such as bash and fish which 
still print `/home/kyle/...`). What is unexpected is that after running 
`pwd -P` all other subprocesses act as if the `cwd` is `/` (though the 
`pwd` builtin and `$PWD` env var do not show any chagne).

To summarize what I am seeing:

```
% ls
test.txt
% pwd
/home/kyle/test
% pwd -P
/home/kyle.homedir/test
% ls
bin  boot  dev	etc  home  lib	lib64  mnt  opt  proc  root  run  sbin	srv 
 sys  tmp  usr  var
% pwd
/home/kyle/test
% /bin/pwd
/
% zsh -c "pwd"
/
% cd .
% ls
test.txt
% /bin/pwd
/home/kyle/test
% pwd
/home/kyle/test
```

Is there a configuration change that I need to make for ZSH or for 
systemd-homed to not end up with an inconsistent cwd state after running 
the `pwd` command?