Weird Exp Loss, First Blood/Kill Trade bug

Second time I or a friend have experienced this bug. Not 100% certain what exactly has to happen, but as far as I can tell, if two champions trade kills, one will randomly just not receive experience.

For example, I was playing Pantheon top vs Teemo. He had just hit 4, I was a minion or two away from 4. We engaged on eachother, His poison killed me, but my turret hit him one last time to clean up the kill. By the time we both returned to lane, he was 5 and I was still 3 with the exact same experience.

My friend encountered the opposite situation in a game just a few moments ago. She secured the kill on Talon as Akali, and then his ignite and bleed killed her. She returned to lane 3, he was still five. This makes no sense. I haven't actively tried to reproduce it but i'm happy to help if I can do anything. This bug is irritating beyond belief, if it is indeed a bug. I wasn't aware of any changes that would make this seem normal, however.