Cmd Dial and call duration limit, warning file

Hi. I’m using Asterisk 1.4.30. Calling party (A) is connected to other party (B) using Dial (e.g., Dial(SIP/XXXXXXXXXXX@provider|60|tL(1680000:60000)m(kzo2)) ), L option is used to limit call duration and to play warning message to both parties.
The problem is that warning message isn’t played to both parties simultaneously. Warning file is played sequentially to caller and callee. When warning file is played to one party, other party hears silence. Is it normal behavior?