Actually, it has two bugs, and one of them inadvertantly provides the solution to the other.
The irritating bug is that if you fill up its "hard disk" then it won't boot (sounds more like a computer than a phone, doesn't it?).
The prophylactic bug is that if you pull the battery out just after turning it on then there's an appreciable chance that it will corrupt its filesystem.
When it has a corrupt filesystem then it boots into a rescue mode that reformats the disk, at which point one can restore from backups.
Quite why it can't have some way of initiating this behaviour sanely, I don't know.
Make that three bugs.