End date not highlighted when it is the first cell on a calendar's grid

To recreate:

Open demo page and go to the first example (where Sunday is the first day of the week, which is key to recreating the bug)
Page through the calendars so that Oct 2015 is the first calendar
Pick any date in Oct as the start date
Drag the range until you are hovering over Nov 1 (should be the first day on the second calendar's grid)

The date doesn't get any highlighting. If you click it as the end date, it correctly recognizes it but the CSS is never applied. Same thing happens under similar circumstances. See, for example, Jan-Feb 2016 on the first calendar on the demo page (where Mon is the start of the week).

onefinestay / react-daterange-picker

End date not highlighted when it is the first cell on a calendar's grid #102