Last summer, our server host finally had to upgrade our machine (it was days away from complete shutdown). The process was extremely rushed, and extremely mis-handled. The whole system went down for an entire day, and there were multiple issues that persisted for quite a while after.
One of these was the calendar bug. On the event calendar feature, if an event was created at a time between 12:01pm and 12:59pm, the time, when saved, defaulted to 6:59pm. Never did figure out why that specific time, but the fix was pretty simple. Somehow, the old server setup accepted over 24 as a legitimate hourly time (so 24:05 worked as 12:05pm). The new server did not allow this- and broke that minor subset of possible times. Once I found that section of code, it was a simple matter to take the substring of the first 2 digits of the time and change them from 24 to 12. Simple- but finding that bug was anything but simple. Particularly for a beginner!