So what is happening is that Month 05 in your data is actually June. As there is no 31st in June, it is being considered as July 1st. Because of this the chart is starting from July 01 23:58 and then moving on to July 01 00:00. This is reason for the oblique line.
Just reduce the month values by one (keeping the range 0-11) and it should work fine.
Tip: You might also want to look at Data/Time formatting if you want Midnight to be displayed as 00 instead of 12.
Thanks for reporting it though. I actually found another bug related to toolTip instead and have fixed the problem. I’ll email you the newer version soon after the doughnut issue is resolved. Public release is couple of days away.