Phones - Why can't I make more than 1 G729 conference call on my Grandstream GXP 2100 when I have multiple G729 channels available?

On Granstream GXP 2100 phones, the phones firmware does not allow more than 1 G729 conference call. This was implemented in Granstream's Firmware Version 1.0.5.14 and up. There is not any way to change this setting through the Switchvox interface.