why new tab I added in dashboard always gone when I get back

I added new tab in my dashboard, but after I re-login, it's gone.
It happens all the time, sooo weird, can anybody help me?

Not only add new tab, any modification on dashboard are not changed. I checked auto-save, it's not working. I unchecked it and saved manually, it's also not working.
I'm using a windows 2008 server, could it possible have reason with that?

Hi. It sounds like there is a problem with the RDF index. Which version are you running? If you're on 3.0.1 or later, could you please run the diagnostics in the JTS admin page? If you see problems saying the index has a problem, it may be the case that the index was copied incorrectly. If this is the case, please backup your index, send us the diagnostics zip by creating a work item and attaching it. Then run repotools-jts -reindex. (you'll need to shut down your JTS).

Let me know how it goes.