Linksys Phone Not Hanging Up

I am using linksys SPA 922 phone on and asterisk pbx. for some reason i cant get it to automatically hang up when i use speaker, for instance if someone call me and i use the speaker phone to pick up the phone when the person hangs up my linksys will remain beeping until i hang it up manually. is there anything i can do to prevent this and have the phone hang up automatically cause i also use some grandstreams and they do hang up automatically when i have it on speaker phone and the other party hangs up. or is this teh way the linksys works?