I found this in kernel.cpp, line 21
// Hard checkpoints of stake modifiers to ensure they are deterministic
static std::map<int, unsigned int> mapStakeModifierCheckpoints =
boost::assign::map_list_of
( 0, 0xfd11f4e7u )
( 10001, 0xd42268a1u )
( 30001, 0x7e0d6e1eu )
( 50001, 0xa5a4473eu )
( 70001, 0xbe5e3360u )
(100001, 0x6cafeba8u )
(133333, 0x011868fcu )
;
Those are PoS checkpoints that shouldn't be there.
The first number is block height, the second one modifier checksum.
My guess is that whenever someone tries to generate block 10001, it doesn't get accepted since
the checksum is different from the hardcoded checkpoint ( 10001, 0xd42268a1u )
To verify if my guess is correct, someone who has been mining could look into his debug.log and
see if there's anything like
AddToBlockIndex() : Rejected by stake modifier checkpoint height=10001