PROFTPD : ls to wrong directory close connection ... Normal behavior ??

Hi !

I have a little problem with ProFTPD.

When I login on my ftp server and issue a command such as

"cd /hgghjg"

and the /hgghjg doesn't exist, it tells me
"550 hgghjg: no such file or directory"

And then I can issue another command without a problem.

But when I do the same with ls

"ls /hgghjg"

I got:

"200 PORT command successful"
"150 Opening ASCII mode data connection for file list"
"450 /hgghjg: no such file or directory"

then when I try to issue another command

"ls"
"200 PORT command successful"
Connection closed by remote host

My connection is closed on the next issued command after I ls to a unexisting directory ....

Is that normal ? Can it be bypassed ?

Help please !