This taken from the Modular Systems website:
“A semi serious bug in the experimental breast physics has been identified that can cause you to permanently lose your body shapes!
If you edit appearance while the feature has been enabled, or is enabled, there is a rare chance that your shape will become permanently broken and missing from database.
Changing shapes while it is enabled, or has been enabled during that session, has also been reported to cause them to go missing from the database.
The other reported problem is that if you click cancel or don’t save during edit appearance you will be unable to wear that shape again until you log in again.
We are investigating the cause of this and hope to soon have a fix. We also encourage people to make backups of the shape they are currently wearing before trying to switch or edit.
EDIT: I’d like to point out that this does not always happen, and actually is semi-rare. We have just gotten enough reports of it happening that we feel it warrented a warning so people are aware that it is an issue that can arise. It only breaks a single copy of the shape, not all instances, and making a copy of the item in your inventory is enough to keep a backup.”
Just sayin for those of you who might care.