Bug in "du", needing current directory

I found an odd bug in using du

Specifically, why does du need to read the current directory if you are 
wanting the disk usage of a different directory.
I ran into this problem because I have a cron job that switches to 
another user, and then runs du in order to do some monitoring. Whenever 
I ran this job as root manually, it worked fine, but when I ran it as 
cron I got the error:

du: cannot open current directory: Permission denied

I eventually figured out that cron was running the process in '/root' , 
which didn't have read permissions set for the user that the process was 
switching to.

It is simple to reproduce this. Create a directory as root and then 
chmod it 700. Switch to that directory and then su to another use 
(therefore you don't have permission to read the current directory) type 
du /etc (or some other directory you normally can access), and you 
should get this error.

My workaround was to give read permissions to /root, but that really 
isn't a preferred method.

# du --version
du (fileutils) 4.1.9
Written by Torbjorn Granlund, David MacKenzie, Larry McVoy, and Paul Eggert.