OMNET++ INET 802.11e Throughput Problem

It seems Omnet++ Inet still has problems with 802.11 mac layer  implementation.  The problem I face is, throughput decreases to half when the Max Contention Window  parameter is set to same value with Min Contention Window. I made the experiment with throughput example supplied in Inet. Simulation environment is set up as 1 AP and 1 Station when cwMinData and cwMaxData is set same value throughput is measured around 2.7 Mbps. Interesting thing is it is same regardless of the value I set (3, 7, 32 …). With 1 AP and 1 Station there shouldn’t be a collision and throughput shouldn’t decrease. I asked forums and reported as bug but still couldn’t find a solution. I guess I’ll be looking for alternative simulation environment, may be ns3?