su 5.2.1 does not invoke bash as a login shell when stdin is from a pipe

[Angel Tsankov]

Hello!

There seems to be a problem with su from coreutils 5.2.1 that 
manifests itself in su not invoking bash as a login shell in the 
following scenario:

root>su --version
su (coreutils) 5.2.1
[...]
root>echo "echo \"This is .bash_profile.\"" >~usr1/.bash_profile
root>cat ~usr1/.bash_profile
echo "This is .bash_profile."
root>echo 'echo $PATH' | su - usr1
/usr/bin:/bin
# NOTE: bash was not invoked as a login shell, which is 
unexpected
root> su - usr1
This is .bash_profile.
usr1>
# NOTE: as expected, bash was invoked as a login shell

Is this really a problem in su and if so, is there a patch for 
it?