Review this KB Article:
Topic Search Engine (SE) fields are cleared out when updating topic
Symptoms
When attempting to edit a topic in the admin console Content > Manage Topics, the Search Engine fields are cleared and do not update.
Cause
This can happen when the store has only one locale set up (this was a known bug that has been corrected in the latest release).
Solution
Go to your admin console Configuration > Localization > Locale Settings menu and add a new locale (ADD NEW button). Be sure to use a valid locale such as en-AU that the software will accept. Edit the topic Search Engine fields you wish to update, save the topic. At this point you can delete the additional locale, but be aware that any edit to a topic without having more than one locale will clear the SE data on that topic again.
Erik Sutton
AspDotNetStorefront Technical Support