Hi Erica,
I tried duplicating the scenario internally with one of our support agents just as you described using the same Mac OS and software versions. Anyone that was joined into the session was able to see the drawings being done from either side, regardless of who was drawing. We could not find any other reports of anything similar from other customers either, so it may be something isolated either to that session or that one presenter possibly.
At this point, the best way to further diagnose what might be happening would be with a call into our support so that an agent and get eyes on the scenario and troubleshoot live. If drawings were working fine for the other attendees until this one presenter took over, having that person on the line as well would be very beneficial.
Phone numbers for calling in to our 24/7 support team can be found here:
http://support.citrixonline.com/en_US/meeting/phoneThanks,
Adrian