So I was on my world, testing this and I found something weird. If I had created an objective and added some points to it then joined a team, the objective would reset to 0 and I am actually unable to gain any more points to that objective, however leaving the teams shows back my first score.
I couldn't add screenshots with mojira so I simply uploaded them to imgur: http://imgur.com/a/gdZSx
The objective is a dummy objective so I am not sure if it does that only for dummy ones or for the others too. I shall go and test.
Edit 1: I have tested it out and discovered that it does this only for dummy objectives. Will attach some pictures.
Edit 2: It seems it happened after I opened LAN. It works perfectly fine now, but it didn't before... So I assume it has to do with multiplayer.
Edit 3: It has been confirmed that objectives get reset to 0 in the list when joining a team and only getting out of the team solves the bug. Happens in singleplayer, LAN and multiplayer.