It seems, the new design and increased font-sizes did something bad to the calendar-popup: See (https://drive.google.com/open?id=0B6Zoc6hWV59YZnEzWjdSU0tZNEk) - it shows up the same way on Mozilla (40.0.2) and Chrome (44.0.).
I am sorry that this is happening. I was unable to reproduce this in any web browser that I had, including Firefox and Chrome. Do you have any browser plugins that might be interfering? Do you have the default font size of your browser increased or decreased?