categories randomly changing into blanks

Today, when I upgraded my blog from 2.2.1 to 2.6.0, all my categories become blanks. In the wp-term table, the ‘stubs’ field had become “-2”, “-2-2”, “-2-2-2”, etc. Now as I work to recreate all the categories for each post, I’ve discovered that some categories with spaces in them are randomly become blank. I noticed this after I logged out and signed back into my blog for further editing. What is going on now with 2.6?

Thanks,
Ron