The type 'windrun' (note the lower-case 'r') is part of group_distance, which was inadvertently left out of the set of groups that get switched when the user selects metric or US (it doesn't appear in any of the skins that are part of WeeWX).
It is easily added. Go into weewx.conf, section [StdReports] / [[Defaults]] / [[[Units]]] / [[[[Groups]]]] and add it. For example,
[[Defaults]]
[[[Units]]]
# The following section sets what unit to use for each unit group.
# NB: The unit is always in the singular. I.e., 'mile_per_hour',
# NOT 'miles_per_hour'
[[[[Groups]]]]
group_altitude = meter # Options are 'foot' or 'meter'
group_degree_day = degree_C_day # Options are 'degree_F_day' or 'degree_C_day'
group_pressure = mbar # Options are 'inHg', 'mmHg', 'mbar', or 'hPa'
group_rain = mm # Options are 'inch', 'cm', or 'mm'
group_rainrate = mm_per_hour # Options are 'inch_per_hour', 'cm_per_hour', or 'mm_per_hour'
group_speed = meter_per_second # Options are 'mile_per_hour', 'km_per_hour', 'knot', or 'meter_per_second'
group_speed2 = meter_per_second2 # Options are 'mile_per_hour2', 'km_per_hour2', 'knot2', or 'meter_per_second2'
group_temperature = degree_C # Options are 'degree_F' or 'degree_C'
group_distance = km_per_hour
I'll add it to the development branch.