Instructions to duplicate the bug:

1) create 12 new test events where start date = 4/23/13 and end date = 4/23/13
2) create 8 new test events where start date = 4/24/13 and end date = 4/24/13
3) Month View, 4/23 lists 4 events & '8 more', 4/24 lists 4 events & '4 more'
4) on 4/23, change test event #10 to end date = 4/24/13 (2-day span)
5) on 4/23, change test event #11 to end date = 4/24/13 (2-day span)

BUG: Month View, 4/23 now lists 4 events & '3 more'

4/24 correctly lists 4 events & '6 more'

Thank you for reporting this bug, Leland! We'll definitely get it fixed ASAP.

Did this ever get resolved? It's been 3 months and no word yet....