Calendar Picker renders dropdown on TOP of the actual calendar

This is happening for ONE user, on ONE computer, on Google Chrome.

When they go to fill in a date field they get a dropdown of seemingly random dates, and after scrolling slightly the dropdown stays in the same location on the screen and the calendar picker appears from behind it.

Has anyone seen anything like this? 

I suspect it's a browser add-on or some Chrome setting that is doing this since it is just for one person and only on their laptop? (I logged in as them and it works fine for me).