I'm conditioning an IPA. After 2 weeks in primary and 2 in secondary all activity had ceased. Then I dry hopped fairly modestly - 75g or so - and 2 weeks into that the thing seems to have gone CO2 crazy. Last night I pulled the Corny valve to equalise pressure. Tonight the keg has enough pressure to dispense very quickly. How can this be happening? The gravity isn't dropping any more from a reasonable 1.012 (from ~1.050), so I don't get what's powering it. Any ideas?!