Marco,
if I restart PL/SQL Developer and try to re-open files (FTP Plug-in, SFTP protocol), I get error message and then empty Command Window opened.
Also, it may be a good idea for files opened via FTP/SFTP to show protocol prefix before filename on title bar, e.g.
[Command Window - sftp://server/path.to/file.pdc]
FTP Plug-in version is 2.0.8, although it says 2.0.7
if I restart PL/SQL Developer and try to re-open files (FTP Plug-in, SFTP protocol), I get error message and then empty Command Window opened.

Also, it may be a good idea for files opened via FTP/SFTP to show protocol prefix before filename on title bar, e.g.
[Command Window - sftp://server/path.to/file.pdc]
FTP Plug-in version is 2.0.8, although it says 2.0.7
Code:
PL/SQL Developer
Version 7.0.2.1079 (MBCS)
01.xxxxx - 10 user license
Windows XP version 6.0 (build 2600) Service Pack 1
Plug-Ins
*FTP File Interface 2.0.7 (C:\apps\PLSQLDeveloper\PlugIns\ftp.dll)
(* is Active)