Inaccuracies In Log Space Reporting

Enterprise Manager reports syslogs space usage as:

Log Size = 800 MB --> The expected value is 0 MB
Log Space Available = 800 MB

The device on which the log has been created is only 800 Mb in size (and not 1600 as the above implies).

I've tried

dump transaction <dbname> with no_log
dbcc updateusage (syslogs)
dbcc checktable (syslogs)
"select count(*) from syslogs" returns 13 rows (a low number as expected)
dbcc opentran reports no open transactions.

The log fills up with very little activity, despite its 800 MB capacity. Can anyone shed some light on this ? Could the problem be caused by a prior dump tran no_log being performed without a subsequent checkpoint ?

regards

doug olsen