i just share my little experiance
there are many kind of lock in android system. verifying according to phone model .
as per example samsung a/c lock, gmail a/c lock , pattern , pin , privacy, face, voice , etc persist at present moment in android system.
of course we can remove all kind of lock like above.
one month ago , i received one china android phone CPU -MTK6580.
phone problem was gmail account lock. just like samsung gmail account lock or samsung account lock.
what a surprise i never seen problem in any china phone like that problem.
i full flash 3 different files , format and all kind job but problem not solve.
i send PM to miracle supporter, CStool supporter volcano and others who are demand big boss in android system .
no answer from any body. no reply. may be they don't know how solve this problem. i back to phone.
today again i received same problem gmail account lock. i try many way but no luck. so, back to phone customer.
if any brother found and face like this problem . pls share.