Minecraft Server save-all does not work as soon as expected

Sorry in advance, this question could fall into 1 of 3 categories (server admin, gaming, or programming)

I'm working on a personal Minecraft server for my friends and I, I'm having the server back itself up on an interval, which requires the commands save-all and save-off to be called in succession before creating the backup file. (afterwards, save-on is called to put everything back to normal)

I'm monitoring the server's output/log to determine when the saving is off so I can create the backup. However, the server's response to my save-off command indicates it is ready, but when I go to make a backup, the world files are modified again, breaking my backup.

So far, my only solution is to add a delay between save-off and backup, but surely I'm either missing something or I can report this to Mojang so it can be handled a bit better. FWIW, I get the same behavior both on the latest stable version, as well as the latest snapshot.

Do save-off or save-all give any other sort of indication as to whether they are fully completed?

NOTICE I've created a bug-tracker issue with Mojang, we'll see what they have to say. 🙂