I just save it as usual. No extensions added or removed.
Yes, I got a backup from the backups folder, I just lost some changes.
I thought I had to report it as bug, just that.
The only unusual thing is that I'm using an external drive (USB hard drive) and I opened it from there.
Without knowing exactly what you did , it is difficult to tell whether this is a bug.
The binary data is corrupt,. so it may also be related to a fault on your harddisk.