mcps_data_request and losses

Hello everyone,
I'm simulating 802.15.4 with ns2.33. As using CBR Traffic sources was
generating unwanted traffic, I switched to calling mcps_data_request from my
Tcl file. This works but there is an issue: when I look at the trace, there
are almost no lost packets. The ratio
(received packets*100)/(transmited packets)
is always close to 100%!!!
When I ran the same scenario using CBR traffic, my hit ratio was 75.08%
So I need to know what is causing this difference: Can someone point to me
what is missing?
Thanks and regards,
R

--
Life is too short to be pissed off all the time.