Mac Calendar Problems

My iPhone, iPad, MacBook Pro, iCloud all accept 24-hour settings for the calendar. I use 13 for 1 p.m., etc.
Recently, iMAC has only allowed single digits for the hour, even for the afternoon, even though the 24-hour setting is in effect in General and Languages and Keyboards. What has gone wrong and how to I correct it?
My default Calendar setting is iCloud and, iCloud on line accepts the 24-hour system figures.

Which version of OS X are you running? I have mine set to the 24 Hr. clock and all my times are in the 24 Hr. format. I'm using the latest Mavericks 10.9.2. BTW, same on my iPhone.

Mavericks, but I discovered the trick: with the system set for 24-hour times of course, first click on "all day" appointment even if you don't mean it, after which, you insert whatever hour you prefer in the 24-hour system. Why it wants to go through that ritual is anyone's guess.

The problem seems to have been fixed upstream.