"Houdini" cronjobs and files on eCryptfs

I'm running vanilla ecrypt-fs of Ubuntu 10.10 and encrypted the whole home directory of the user "user".
The encrypted home is generated with "ecryptfs-migrate-home -u user". No additional configuration.
The ecryptfs mount looks like this:
/home/user/.Private on /home/user type ecryptfs ....

I have a script inside the encrypted home called /home/user/garbage.sh containing the following line:
/bin/date >>/home/user/garbage.out

Now I'm creating a cronjob with the following crontab entry:
0-59 * * * * /home/user/garbage.sh

The cronjob runs as expected when I'm logged in.
I logout and the ecryptfs mount disappears as expected.
"ls -l ~user" as root lists no garbage.* files.
Now I would expect that cron would fail to locate the script after I logout.
But this is not the case. The cronjob continues to run and is writing the timestamp every minute.
If I login again, I find the timestamp correctly written into the encrypted file. How is this possible?

Logging out again as user "user".
Now when I terminate cron (service cron stop), the cronjob is not executed anymore... this is expected.
I'd expect (again) that cron does not find the script when I re-start cron shortly after it's termination.
But now (at least to me) the unexplainable happens:
1. The cronjob continues to be executed.
2. The script continues to write timestamps into the encrypted file.

Logging in again as user "user" verifies: The timestamps were written to the file when user "user" was not logged in
and ecryptfs was not mounted.

Could anybody explain this trick to me?
It looks like a bug to me, but I want to make sure it's not a feature...
Thanks in advance!