Trends in the acid strength of oxoacids

I was working on a problem regarding the relative acidity of oxoacids in the form $\ce{HYO3}$ where $\ce{Y}$ represents a group 17 element.
The question (which is from a worksheet created by a chemistry instructor at my institution) is as follows:



> 
> Which of the following is the most acidic: $\ce{HBrO3}$, $\ce{HFO3}$, $\ce{HIO3}$, and $\ce{HClO3}$?
> 
> 
> 


The given answer is $\ce{HIO3}$. However, in my understanding, the acidity of oxoacids is driven by bond polarity, which is affected by the electronegativity of atom $\ce{Y}$, as [this question](https://chemistry.stackexchange.com/questions/9401/halogen-oxyacid-trend-acid-strength) suggests. For oxoacids of the same structure, only differing in the atom $\ce{Y}$, I believed that the acid strength increases as atom $\ce{Y}$ increases in electronegativity. Thus I believed that $\ce{HFO3}$ would have the greatest relative acid strength. As a matter of fact, I believed that $\ce{HIO3}$ would have the lowest relative acid strength as $\ce{I}$ is the least electronegative of the four $\ce{Y}$ atoms on this list. I would appreciate it if you could help me understand why this anomaly, that $\ce{HIO3}$ is stronger in acidity than $\ce{HFO3}$ contrary to the general trend regarding the electronegativity of $\ce{Y}$, applies in this case.


