Unexpected behaviour on output redirection after update to 20.04

[ubuntu-users-list at thomas.freit.ag]

Hi,

since I updated from 19.10 to 20.04 on two machines, I have an unexpected behavior on output redirection, which fails for root (and worked before with 19.10):

To reproduce:

1) create a file as user:
user at host:~$ echo `date` > /var/tmp/testfile
user at host:~$ ls -l /var/tmp/testfile
-rw-rw-r-- 1 user group 33 Apr 26 20:56 /var/tmp/testfile

2) redirect output as root to that file (append a line):
root at host:~# echo `date` >> /var/tmp/testfile
zsh: permission denied: /var/tmp/testfile

I would expect, that root could just append to any file on a local filesystem (ext4 in this case). This happens in bash as well.

Any idea, what is the cause for this?

Regards,
Thomas