Vault automatically trims leading and trailing spaces of a value in an object or document field upon saving. If there is a leading/trailing space in the value of the field, it is the result of an en-US space character, which is different than a standard space. Vault treats the value of en-US space as a valid character and does not remove it from the saved field. 

Note: This often occurs when a value is copied and pasted into a field.