New Post: "Required" flag on MultiKeySelector is being ignored (i think)

I'm attempting to use the <MultiKeySelector> within a Form XML for a Page Metatype but now whenever i attempt to save a page with the additional Metadata properities on it I can't because it's telling me the field is required. This is what the xml for the fields looks like in the file:

<MultiKeySelector Label="Categories" Help="" OptionsKeyField="Id" OptionsLabelField="Name" Required="false" CompactMode="true">
                <MultiKeySelector.SelectedAsString>
                    <cms:bind source="Categories" />
                </MultiKeySelector.SelectedAsString>
                <MultiKeySelector.Options>
                    <ff:StaticMethodCall Type="ESI.C1.Services.TagQuery, ESI.C1.Services" Method="OfType" Parameters="Categories" />
                </MultiKeySelector.Options>
            </MultiKeySelector>

Also, here's the form binding line:

<cms:binding name="Categories" type="System.String" optional="true" />

What am I missing? Why is it still telling me the field is required, I don't want it to be.

thanks!