SunbirdPortable.ini : AllowMultipleInstances=true doesn't work at all.

Hello,
i would like to launch multiple instance of sunbird, so i looked in 'SunbirdPortable.ini' and found 'AllowMultipleInstances=false'. i've change it to 'AllowMultipleInstances=true'.
But it doesn't change anything.
Sunbird say:
"sunbird is already running, but is not responding. To open a new window, you must first closethe existing Sunbirdprocess, or restart your system."

I've look for something in sunbird and found 'parent.lock' in 'data/profile'. it seems to lock sunbird, and prevent it to have multiple instances.

Is this means 'AllowMultipleInstances' never work ?

Thanks