Strange 'su' error messages

[Christian Schuerer <csw@xray.at>]

Hello!

Since updating my debian server yesterday I get the following error
messages every hour (generated by logcheck):

  Jan 13 00:05:01 asterix su[2102]: + ??? root:bin

Today there is even an additional line:
  
  Jan 13 06:05:01 asterix su[5684]: + ??? root:bin
  Jan 13 06:25:01 asterix su[5741]: + ??? root:nobody

Does anyone have the same error messages/behavior? I'm concerned, but
hope that it's just a wrong configuration after the update!

I'm thankful for any help!

Regards,

  Christian