Sam,
This is normal OBi behaviour. Looking at the InboundCallRoute:
Voice Services -> OBiTALK Service -> InboundCallRoute:
{(290123456)>(Msp1):sp1},{(290123456):aa},{ph}
This rule {(290123456):aa} says if no digits, or digits that are not recognised, are received from the softphone number, then connect the call to the Auto Attendant.
If you have no need for the aa, then you could simply delete the rule and have:
Voice Services -> OBiTALK Service -> InboundCallRoute:
{(290123456)>(Msp1):sp1},{ph}
If you would like access to the aa, then you could set up a code such as:
Voice Services -> OBiTALK Service -> InboundCallRoute:
{(290123456)>(Msp1):sp1},{(290123456)>**0:aa},{ph}
This would allow access from the OBiON app to the aa by dialling **0 - same as from the phone connected to your OBi.