Bind with ProFTPd and OpenBSD 2.4

[Federico Giannici <giannici@neomedia.it>]

I have a problem with ProFTPd 1.2.0pre3 in a OpenBSD 2.4-Release i386.

Sometimes it drop connections with clients that issue a "LIST -L"
command.
The following errors are generated:

Mar 10 19:43:02 aragorn proftpd[23609]: attempted bind to
195.120.250.20, port 20 
Mar 10 19:43:02 aragorn proftpd[23609]: bind() failed in
inet_create_connection(): Interrupted system call 

It happens only with some clients (I presume only with those that don't
use a passive connection) and only sometime, so it is hard to reproduce:
a moment it works and some minutes later it doesn't work any more.

Tried with ProFTP 1.2.0pre1 to 1.2.0pre3, but the problem remains...

Somebody else had the same problem?
What can I try to solve it?

Thanks.