This bug has been added to the tracker:
https://winscp.net/tracker/772

Thanks for your post. I have sent you an email with debug version.

Sometimes after lost connection and successful reconnect I have error message about problem with memory. debug2-log has strings:
~~~~~~~
< 2011-11-14 20:45:20.408 drwxr-xr-x 2 root psaserv 4096 2010-02-19 15:41:20.000000000 +0000 web_users
. 2011-11-14 20:45:20.408 Read 30 bytes (0 pending)
< 2011-11-14 20:45:20.408 WinSCP: this is end-of-file:0
. 2011-11-14 20:45:20.409 Directory listing with --full-time succeed, next time all errors during directory listing will be displayed immediatelly.
. 2011-11-14 20:45:20.409 Startup conversation with host finished.
* 2011-11-14 20:45:20.555 (EAccessViolation) Access violation at address 0059D9C4 in module 'winscp505.exe'. Read of address 00000000
. 2011-11-14 20:45:20.568 Session upkeep
. 2011-11-14 20:45:20.568 Looking for network events
. 2011-11-14 20:45:20.568 Timeout waiting for network events
. 2011-11-14 20:45:21.011 Session upkeep
~~~~~~

Windows 7 32bit
WinScp 5.0.5