Why the fields in the pivot chart change?

Why the fields in the pivot chart change?

Hello Everyone.

My question is: Why in the pivot chart, the fields change it's name? in the translation, and in the form, and in the report the name of the fields are good, but when i created the pivot chart the fields appear like: "Number" , "Number3" or, the name that i have for the date is "Fecha" but in the pivot chart appear with the name of the last field that i created in the form... I saw the translation and everything possible to correct this and i can't find something, help me please, IT'S URGENT!