How do we stop the date selector from moving around the screen?

We have a number of project boards where we need to adjust the date in the due date column. The template was set up back in March and we want to a) have the start date be the date the project board is created not the date on the template and b) stop the calendar date selector from jumping all over the screen! You can use right and left to move months but the whole calendar box moves around the screen causing issues selecting dates. Is there a fix for either of these date issues?