Hi,
I honestly don't have a good solution for this problem. The whole thing is very complicated to make events that span across days on the calendar, it involves very complicated use of colspan and rowspan on cells and lots of padding rows to make it work correctly but it still can't render perfectly for every possible combination of events. Basically the space you are seeing there is because the 5 day event is using rowspan="2" in order to make the table markup correctly with the right number of rows and columns, but the div inside that td is what has the border but it doesn't take up the whole height of the td and the td has no bottom border so it makes it look like the side borders don't go all the way up but they do go up to the bottom of the td, just not to the bottom of the div.
I've tried various things like setting the height on the div to 100% but this doesn't work unless the td has a specific height on it and doing that only makes other problems.
I wish I had a better solution but I'm afraid this implementation is the best thing I could come up with and I acknowledge it isn't perfect.
Best,
Joe