I have metric setting and laps are shown in km but the treadmill laps are 1.6km equal to a mile instead of 1km.
Set the auto-lap distance to 1km in the activity profile settings
In my forerunner 45 I can only set autolap on or off. not distance.
Are you sure you have enabled the metric units directly on the watch (not only in Garmin Connect)? If so, try disabling and re-enabling the auto-lap option.