Has anyone ever seen this?

The local SYSTEM account keeps removing the Logon As account used by
SQL (and only SQL) out of SQL groups

For example:
Event Type: Success Audit
Event Source: Security
Event Category: Account Management
Event ID: 637
Date: 6/28/2007
Time: 4:01:55 AM
User: NT AUTHORITY\SYSTEM
Computer: COMPNAME
Description:
Security Enabled Local Group Member Removed:
Member Name: -
Member ID: <dom>\<ServiceAccount>
Target Account Name: SQLServer2005MSSQLUser$COMPNAME$MSSQLSERVER
Target Domain: COMPNAME
Target Account ID: COMPNAME\SQLServer2005MSSQLUser$COMPNAME
$MSSQLSERVER
Caller User Name: COMPNAME$
Caller Domain: <dom>
Caller Logon ID: (0x0,0x3E7)
Privileges: -

Turns out the system was having troubles trying to auto install SP2. I
just manually installed, and everything is fine now.

--Gene