It appears that adding a basic tolerance to a dimension (i.e. box around the dimension value) locks in the dimension precision. If I add a basic tolerance and try to change to a different precision (e.g. 2 decimal places instead of 1 decimal place) the value remains at its current precision level.
Does anyone know if this is intended behaviour of a basic tolerance? Help file doesn't mention anything of the sort so I'm guessing it might be a bug.