I have experienced that someone can DoS a player off the server with a lot of Trade Requests. So here is the backtrace I got while reproducing it:
Program received signal SIGABRT, Aborted.
[Switching to Thread -1220607840 (LWP 30577)]
0x41e9384b in raise () from /lib/tls/libc.so.6
(gdb) bt
#0 0x41e9384b in raise () from /lib/tls/libc.so.6
#1 0x41e94fb2 in abort () from /lib/tls/libc.so.6
#2 0x42a38317 in __cxa_call_unexpected () from /usr/lib/libstdc++.so.5
#3 0x42a38354 in std::terminate () from /usr/lib/libstdc++.so.5
#4 0x42a384c6 in __cxa_throw () from /usr/lib/libstdc++.so.5
#5 0x4216ba44 in gcn::Widget::hasModalFocus () from /usr/lib/libguichan.so.0
#6 0x42160f0b in gcn::FocusHandler::requestModalFocus ()
from /usr/lib/libguichan.so.0
#7 0x08075529 in FocusHandler::releaseModalFocus (this=0x821e4c0,
widget=0x83de458) at gui/focushandler.cpp:54
#8 0x4216b910 in gcn::Widget::releaseModalFocus ()
from /usr/lib/libguichan.so.0
#9 0x4216a671 in gcn::Widget::_setFocusHandler ()
from /usr/lib/libguichan.so.0
#10 0x42169b7e in gcn::Widget::~Widget () from /usr/lib/libguichan.so.0
#11 0x421829da in gcn::Window::~Window () from /usr/lib/libguichan.so.0
#12 0x080afc07 in ~Window (this=0x83de458) at gui/window.cpp:116
#13 0x08094707 in ~RequestTradeDialog (this=0x83de458)
at gui/requesttrade.cpp:74
#14 0x080b0db3 in WindowContainer::logic (this=0x820e478)
at gui/windowcontainer.cpp:35
#15 0x421642b0 in gcn::Gui::logic () from /usr/lib/libguichan.so.0
#16 0x080793ab in Gui::logic (this=0x820e3e0) at gui/gui.cpp:199
---Type <return> to continue, or q <return> to quit---
#17 0x080cb826 in game () at game.cpp:227
#18 0x080d4c47 in main (argc=1, argv=0xbffff8f4) at main.cpp:429
This was made through a special prepareted client so it might be falseyfied, because this time also my frame rate got down, the times before it didn't but I also ran an sdl version without debuging symbols.
The next thing is while I tried it with an usual client - better a usual player tried to DoS me with trade requests (I asked him to do it!) a Trade Window Opend but neither he nor I could close it, the only way to get rid of it was to reenter the game.