Time Machine not detecting changes in certain folders

I recently noticed that TM does not update its backup from certain folders any more.

I have a deep sub folder inside ~/Documents, and when I create new folders or files in it, they do not appear in the TM backup. The backup contains, however, lots of files created until Oct 2, 2013. Which means that TM used to backup the contents of this folder.

Now, before you suggest that I have probably disabled backup for this folder - nope:

• When I check with tmutil isexcluded for paths of files that didn't get backed up, it says [Included].
• When I then added another disk as a second backup destination, that backup does contain the missing files. This proves that the source is accessible and can be backed up. So, any suggestions that the path may contain invalid chars or is too long doesn't apply, either.

Somehow the existing backup got stuck, preventing it from updating these particular folder contents.

• The system log does not show any messages related to this.

• A disk verification with Disk Utility does not show errors, either.

I could just erase the entire backup and start over, but I would rather not lose my previous versions.

Any ideas how to possibly "reset" or fix the backup so that it backs up the missing files again? I suspect that there's some kind of database that TM maintains to be able to quickly browse its backup folders, and maybe that's corrupt somehow, but I cannot find one.

Here's another idea: If the source disk was modified without OS X watching over it (thru fsevents), e.g. by booting from another system, the TM detects this and starts a complete comparison again, right? I wonder if I can trigger that, and that this will fix the issue.

In the past I've seen knowledgeable people indicate that TM backups can get broken once the backiup gets full and needs deletion of old versions (this is the case here), but no one was able to explain what exactly goes wrong and whether this can be fixed. If you know more details, please comment. I just might write a tool for that in the end :)

(I am an advanced Mac user and programmer; I am using 10.9.3)

Solution 1:

What actually helped was to identify the folder inside which no file changes were detected, and then rename that folder and force a backup. Then all new content inside it got added to the old backup. After that, I renamed the folder back to its original name, added another file inside and did another backup - again, the new file got backed up.

So, somehow, that folder got stuck, and by renaming it, I could reset the backup for it.

Still, I will keep an eye out for other folders that may not get backed up, using the tmutil compare command regularly.

You just can't trust Time Machine.

That's why I also use CrashPlan as a secondary, and offline, backup.