If you are the only person seeing this behaviour, it is likely a bug in their system.
Many ages ago, on one of the most popular mail and news systems of the day, it turned out that myself and another person both managed to register the same username, each with a different password, but were assigned to the same account.
After a couple of weeks in which each of us would log in, see the changes the other did, undo them, change our own password, and mail the abuse team (which kept replying "no, we see that you did it yourself on xxxx"), we both realized what had happened, and started talking by emailing ourselves. Eventually, the other guy left the account to me (I had it for 2 years when he managed to register it).
Many ages ago, on one of the most popular mail and news systems of the day, it turned out that myself and another person both managed to register the same username, each with a different password, but were assigned to the same account.
After a couple of weeks in which each of us would log in, see the changes the other did, undo them, change our own password, and mail the abuse team (which kept replying "no, we see that you did it yourself on xxxx"), we both realized what had happened, and started talking by emailing ourselves. Eventually, the other guy left the account to me (I had it for 2 years when he managed to register it).
It could just be a bug, rather than malice.