I believe I have the same issue.
New events made in calendar change back to default information after a few seconds, I need to go in again and modify the information for event, location, time, etc. After that second time it works. This is getting annoying, please help.
Early 2011 15" MacBook Pro
OS X 10.9.5
2.2 GHz intel i7
6GB 1333 MHz DDR3 Ram
AMD Radeon HD 6750M 512 MB graphics.