ampsrc
No idea, I'm thinking maybe a UI glitch. You can check the database to confirm if it's enabled or not by going to the ost_email table, copy the id for the email in question, go to the ost_email_account table, lookup the records where email_id equals the id you copied from the previous table, and look at the active value for the associated records; this should be set to 1 if they are Enabled and 0 if they are Disabled. If it shows Enabled in the database then you can try refreshing the page, clearing cache/cookies/session, etc.
In order for email fetching to function properly you need to have Admin Panel > Emails > Settings > Email Fetching set to Enabled and you need to have a cron job configured and running.
Cheers.