Default 5Ghz WIFI CANNOT AUTO CONNECT ISSUE

My S3 MINI is DMOD V6 ROM.
I connect a 5g wifi hotspot it's successful.But I turn off wifi and turn on again,it's cannot autoconnect to the 5g hotspot.Must click "connect" it will connected.
2.4G hotspot is normal , it's can autoconnect when turn on wifi.
what is the problem?thanks.
AND...On my samsung galaxy tab 10.1(P7510) with stock 4.0.4 ICS rom, it's normal,can auto connect to 5G hotspot when turn on wifi.