remove the current directory

Can I remove the current directory?

I used to believe you cannot.

Solaris:

$ uname -s
SunOS
$ mkdir /tmp/bla
$ cd /tmp/bla
$ rm -r /tmp/bla
rm: Cannot remove any directory in the path of the current working directory
/tmp/bla
$

AIX:

$ uname -s
AIX
$ mkdir /tmp/bla
$ cd /tmp/bla
$ rm -r /tmp/bla
rm: Cannot remove the current directory /tmp/bla.
$

Today I did a rm that I expected to fail, but …

$ uname -s
Linux
$ mkdir /tmp/bla
$ cd /tmp/bla
$ rm -r /tmp/bla
$ 

Wait, did it work?

$ cd /tmp/bla
$ pwd
/tmp/bla
$ cd /tmp/bla
$ ls -lad /tmp/bla
ls: /tmp/bla: No such file or directory
$ cd /tmp/bla
$