flash disconnects calls -call waiting issue

[et_phone_home]

I'm using two SIP providers with my obi110.
SIP 1 for outgoing calls, and SIP 2 for incoming. When there's a call waiting beep during a call made using SIP 1, and I hit the flash button, obi does not switch to the incoming call on SIP2. I get a dialtone . hitting flash again, I get a dial tone again ....disconnecting the original call.

help appreciated.