Oh, are you sure it always happens with certain accounts? If so, I might have a clue as to what could cause it. During early internal beta testing periods, we had a bug with certain accounts which was hard to reproduce, until we figured out that it's caused by entering first letter as capital when you log in. However, this was fixed since a long time ago, but it might still be some combination involving mix of lowercase and uppercase. If possible and if you have somebody affected by the issue, try to log in with all lowercase and see if that fixes it. If not, I'm afraid there are no logs for such situations. Anyways I'm sure we will find the cause, it will just take some time but it's definitely something that needs fixing before the stable release.