Problem with VSFTPD local_max_rate on Knoppix 3.8.1

Hello,

When I use the local_max_rate option in vsftpd.conf, the transfers just block and never finish.

Here is my configuration file :
local_enable=YES
dirmessage_enable=YES
xferlog_enable=YES
connect_from_port_20=YES
listen=YES
local_max_rate=10
trans_chunk_size=8192

Thanks in advance for your help.