Navigation speed limit units change

I have the UK Toyota navigation package and every now and then the units for the speed limits change from miles per hour to kilometres per hour. The effect is short lived and it will change back on its own. It does not affect the voice warnings when travelling too fast except that the warning will say, for example, the speed limit is 48 kilometres per hour rather than the expected ...30 miles per hour. Has anyone else had this happen (it may only be possible with European maps).

 

Hum, 6.7.0WH. Might need to look at that. Thanks.