I am also having this problem when using xrdp 0.5.0 when connecting to Ubuntu 11.10.

I am not sure how to reproduce the error, but when it happens it seems like the alt key is stuck being held-down. The only way I can click items is if I hold down control.

The only way to fix it so far is to logout of the user account and disconnect the rdp session. Upon re-login the issue is corrected (until it happens again)

$ ps ax | grep xrdp
8752 ? Sl 4:59 /usr/sbin/xrdp
8754 ? S 0:01 /usr/sbin/xrdp-sesman
16136 ? S 0:00 /usr/sbin/xrdp-sessvc 16138 16137
16157 ? Sl 0:00 xrdp-chansrv
21112 ? S 0:00 /usr/sbin/xrdp-sessvc 21114 21113
21141 ? Sl 0:00 xrdp-chansrv
21424 ? S 0:00 /usr/sbin/xrdp-sessvc 21426 21425
21445 ? Sl 0:00 xrdp-chansrv
21992 pts/1 S+ 0:00 grep --color=auto xrdp

$ /usr/sbin/xrdp --version

xrdp: A Remote Desktop Protocol server.
Copyright (C) Jay Sorg 2004-2009
See http://xrdp.sourceforge.net for more information.
Version 0.5.0