ioFTPD gives a PASV port out of the range

[Mr_X]

I got a problem when using PASV mode (I can't use active mode because I'm in a local network and my modem-router don't open ports [there's a bug in the firmware; I'm not the only one to have this thing]). I have this in ioFTPD.ini:

...
[Any]
Bind=0.0.0.0
Ports= 10000-10004
...

REM: You may say it's not enough but there's maximum 1 user connected
It must all the time use ports between 10000 and 10004.
Nearly 4/5 attempts get a port in this range but sometimes I got another port (more than 3 times higher than specified).
For example (Server side): "227 Entering Passive Mode (xxx,xxx,xxx,xxx,128,185)" that mean port 32953 which is not between 10000 and 10004.
For those who don't know how to know what port is given, here's an explanation: You multiply the fifth number by 256 and you add the last and then you get the port used (The four first number are, of course, IP address).

My question is: why does io try another port than those specified in configuration file?

[Mouton]

U should setup at least 10 pasv ports by simultaneous user.
A used port is not closed as soon as the connection is closed; it takes somewhere between 2-10 seconds to be available again.
Hit CTRL-R 5 times in a row, and u'll be out of ports. Same would happen if you browse directories at a decent speed.
Maybe io choose a random port when the pasv ports u specified are all in use.
Try to "netstat -n" very rapidly when u get a higher port. U might see connections on all the other ports from your range.