Djm34 build sends normal shares and previous block's shares.
Those previous block's shares are totally useless and treated as invalid. So it's intended action actually.
I believe that invalid share percent goes up and down radically. It should be okay most times, isn't it?
Yes you right, checked more times and invalid % used to be considerably lower; and rewards looks good based on previous calculations so all ok

Just 1 more question:
Any way to check average hashrate for a specific pool(for example for 24h)? I cant find it
Thanks in advise