In HOF, why does fluorine has +1 oxidation state? Why is there such an anomaly?

Fluorine exhibit +1 oxidation state.
Structure of HOF is 
HO- F
Let the oxidation state of fluorine is +1. Oxidation state of OH is -1. Overall charge on compound is zero.
x -1 = 0
x = +1
So, oxidation state of fluorine is +1.