obi110: POTS Call Waiting doesn't work

[Lynx]

I use my Obi110 for POTS incoming/outgoing and SIP outgoing-only.

When I am on the POTS line and get an incoming call, I hear the call waiting tone. But when I press "Flash," I get a dial tone instead of the other caller. The incoming call continues to ring for the caller on the other end.

Call waiting works fine when I bypass the Obi110 and plug the phone straight into POTS line.

Is there a setting I need to change to get POTS call waiting working on the Obi110?

[Everton]

I think you have to do a DOUBLE Flash in quick succession to pick up the second incoming call.