Fence gate opening problem

Put the summary of the bug you're having here
My fence gates keep opening by themselves.
What I expected to happen was...:
I made a farm and put fence gates on it. After a little days of leaving them in the closed position ( not checking it everyday) I came back and expected to see them closed.

What actually happened was...:
After assuming they were still closed, all of them were open and I did the same thing multiple times(in some minecraft days) just to see if it was me or if it would happen again. It did and it let a couple of my farm animals away.

Steps to Reproduce:
1. Set down a fence gate(make sure in closed position)
2. Leave it alone for 5 minecraft days(not checking on it)
3. See if it has opened even though you didn't open it