Very slow bitcoind callback

[Gimmoroy]

server=1
daemon=0
testnet=0
rpcuser=xxxxxxx
rpcpassword=xxxxxx
prune=4000
maxmempool=200
maxconnections=8
rpcthreads= 12
minrelaytxfee=0.0005
limitfreerelay=5
dbcache=50
walletnotify=/var/www/ClientServer/wallet-cb.sh %s
settxfee= 0.0005
maxtxfee=0.0016

I send some amount to bitcoind ( precompiled 13.02 under deb 8/64), then manually check the transaction. Bitcoind knows about this transaction at a moment and shows correct info on gettransaction, but it send walletnotify only 8 minutes later!

Sometimes it doesn't send first notification (0 conf) at all, but only for 1st confirmation (one time). 

Why?