In 19.3.6 is the example:

For example, given a user-defined type my:coordinates defined as a list of xs:integer with the facet <xs:length value="3"/>, the expression my:coordinates("2 -1") will return a sequence of two xs:integer values (2, -1), while the expression my:coordinates("1 2 3") will result in a dynamic error because the length of the list does not conform to the length facet. 

The intended xs:length value should surely be 2 rather than 3.