I'm having the same problem on Huawei U8652 running Android 2.3.6. All events entered via phone disappear roughly 1 minute later, apparently with the next sync. I can actually watch the event disappear from my calendar. I've entered events of 1-hour duration, all-day duration, and just attempted entering an event using a different time-zone (e.g., London, UK). The calendar posted it, briefly, placing it in my calendar adjusted for the time difference (I set the event for 9am GMT, it appeared on my calendar at 5am EDT). It disappeared like all the others.
An event I entered yesterday morning for next March 15 (2016), I see, is also missing -- so this problem existed, at least for me, as early as yesterday. Upcoming events in the coming months that were entered weeks ago still appear properly. It is only events entered today or yesterday that have disappeared.
Events I enter via Google Calendar on my laptop appear just fine, and persist -- they haven't disappeared. Only those entered via my phone vanish.