I have a datefield where I have set the maxValue as current year like so:

 maxValue:  "12-31-"+ new Date().getFullYear()
and although this keeps me from selecting a date past 2017 it does not show those dates as greyed out. Nor does it remove years 2018 and beyond from the dropdown menu from which you can jump to month/year.

This is not reproducible in 6 and if I remember correctly 4.

I dont have a fiddle but you can test directly in the datefield API editor: https://docs.sencha.com/extjs/5.0.1/...ield.Date.html