Except this is an opposite effect type of logging....  

For instance, you log going off duty.... then you show you have had enough time off before you cao come on again, except you've WORKED between logging off duty and coming back on.   So, you aren't showing that you have enough time off, when you snuck in some duty time in there after you've logged off!

You're log is not to be trusted if they see you've worked and have not shown corresponding duty time.   POI's can cross-reference training records (ground school), safety meeting rosters, pay/travel records, etc to easily see your DUTY report is not accurately reflecting your actual DUTY time.

Company assures FAA/POI their duty time reports are designed to ensure pilots meet the FAR requirements, but that only works when pilots are actually reporting their DUTY times!

Travel for the company, training, meetings, etc are DUTY!