Why the search rules are not the same on the fields "Keyword(s)" and other fields in search engine.

I have 3 fields in my search engine :

• Keyword(s)
• Name
• Lastname

If i set "LE PRIOL" in Keyword(s), it will returns only users pages containing "Le Priol"

If i set "LE PRIOL" in Name / Lastname, it will returns the union of all users page for which the Name / Lastname contains LE and PRIOL (numerous results)

It should be the same rule than for Keyword(s) no ?