I've found a bug in the issue tracker of Mojang, Jira, I'm reporting it here. I hope you'll send to Atlassian in order to fix it.

What I did
In a "Created vs. Resolved Issues Report" (see 1.png),
if an issue is closed at 12:59, then it is counted correctly into the row of 12:00 (see 2.png).
In the example there are 3 issues.
If I click the number 3, the following URL is generated:

https://bugs.mojang.com/issues/?jql=project+%3D+MC+AND+resolutiondate+%3E%3D+%222018-07-03+12%3A00%22+AND+resolutiondate+%3C%3D+%222018-07-03+12%3A59%22

The bug
The issue closed at 12:59 is not visible into the list, see 3.png.
Issue not visible: https://bugs.mojang.com/browse/MC-131903

Workaround
Edit the search query, as shown in 4.png.