terminal window in konsole sometimes hangs

Sometimes a terminal window of konsole just hangs/freezes when hitting tab for zsh completion. Using konsole specific keycodes (like to open a new terminal window) are still possible, scrolling in the affected terminal window as well. I'm not 100% sure if this is not partly fault of zsh, but running zsh in xterm doesn't cause such hangs. What's really strange is that hitting backspace hard sometimes "unfreezes" the terminal window.

backtrace:
Thread 1 (Thread -1233418048 (LWP 7121)):
#0 0xffffe410 in __kernel_vsyscall ()
#1 0xb7d2014d in select () from /lib/tls/i686/cmov/libc.so.6
#2 0xb6bb9802 in QEventLoop::processEvents () from /usr/lib/libqt-mt.so.3
#3 0xb6c2cd03 in QEventLoop::enterLoop () from /usr/lib/libqt-mt.so.3
#4 0xb6c2cb22 in QEventLoop::exec () from /usr/lib/libqt-mt.so.3
#5 0xb6c14267 in QApplication::exec () from /usr/lib/libqt-mt.so.3
#6 0xb7f18458 in kdemain () from /usr/lib/libkdeinit_konsole.so
#7 0x0804846a in ?? ()
#8 0x00000001 in ?? ()
#9 0xbfde16f4 in ?? ()
#10 0x00000000 in ?? ()

konsole: 4:3.5.3-2ubuntu8 (i386), but also with the latest dapper version