Why does Full Text Search get this result?

Question

A Full-Text query like this one:

SELECT *
FROM TABLE1
WHERE CONTAINS(COL1,'"x* ray*"')

gets all rows containing any combination of x and ray but not one without the other. If we modified the query this way

SELECT *
FROM TABLE1
WHERE CONTAINS(COL1,'"x* ray* "') --With a space after ray*

it gets all rows not only containing any combination of x and ray but also all rows containing ray without x what is wrong with the space at the end.

Thank you for any help.