Oops. The option was gone again in a few minutes while I'm online.
I think Amazon service keeps calling home, and reverting values back.
I found out that my extra_identifiers table now have only one record, the 'KINDLE_EINK_REMOTE_LICENSE_RELEASE_V2' row was gone!
Code:
sqlite> select extra_identifier, poll_interval from extra_identifiers;
DecanterChromeV1|30
sqlite> select extra_identifier, experiment, treatment from experiments;
DecanterChromeV1|DECANTER_CHROME_V1_FALLBACK_328845|C
DecanterChromeV1|DECANTER_CHROME_V1_MALBEC_FALLBACK_370896|C
sqlite> .exit
Manually insert of the missing record back doesn't restore it back. After reboot, it will have only one record. (T_T)