Exchange 2007 Online Maintenance Overlap

Every night at 02:59 the following events are logged by my Exchange server:

Event Type:   Warning Event
Source:       MSExchangeIS Mailbox Store
Event Category:  Background Cleanup 

Event ID:       9871 
Date:           5/20/2009
Time:           2:59:59 AM 
User:           N/A
Computer:       EXCHFC2 
Description: There is an online maintenance overlap for database "First Storage Group\Mailbox Database". Please revise the online maintenance schedule.

For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.

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Event Type: Information
Event Source:   ESE
Event Category: Online Defragmentation 
Event ID:   704
Date:       5/20/2009
Time:       2:59:59 AM
User:       N/A
Computer:   EXCHFC2

Description:
MSExchangeIS (12420) First Storage Group: Online defragmentation of database 'C:\Program Files\Microsoft\Exchange Server\Mailbox\First Storage Group\Mailbox Database.edb' was interrupted and terminated. The next time online defragmentation is started on this database, it will resume from the point of interruption. 

For more information, click http://www.microsoft.com/contentredirect.asp.

This is Exchange 2007 running on Windows 2003 x64.

Here's my Exchange maintenance schedule:

First Storage Group\Mailbox Database: 20:00 - 03:00  
Second Storage Group\Public Folder Database: 03:00 - 06:00

Note that I tried spacing them out more (First ended at 2, second started at 4) to no avail. The error message always appears a second before completion of the First Storage Group's maintenance plan.

The interrupted defragmentation noted in that second event was begun at 02:15. Another defragmentation of the exact same database was begun at 23:04 and finished at 02:08. Immediately before this full defragmentation, the interrupted one from last night was completed.

So it's as if the system is defragging the database in a loop, then complaining when that defrag is interrupted by the conclusion of the maintenance window.

How can I fix this behavior?

EDIT

My backups run at 06:30. There are no scheduled jobs on this machine.

The Best Practices Analyzer reports nothing relevant.

I understand that this is not a critical error, but I'm concerned that if I simply ignore it I'll overlook a future problem when maintenance is NOT being adequately performed. In that vein, I'd like to resolve whatever is causing the defrags to loop during the maintenance window.