New invoicing - Calendar to remain stagnant when moving through months
When you open the calendar to input a date (e.g., expense claims), the calendar box changes shape/moves around when you click the arrow to go back over previous months because the number of days in each month varies. The calendar shouldn't move around because you must keep repositioning the cursor to find the arrow again.
As someone mentioned in another comment, allow the ability to use the mouse scroll to go back and forth.

Hi Kelly, if you're still experiencing issues with this I would recommend connecting with our specialists at Xero Support via Xero Central to take a closer look and confirm if working as designed.
We made a few changes to the calendar a few month back that I believe will have resolved any issues you were having with the calendar moving around like you've described here. Thanks