Version:            (using KDE 4.2.3)
OS:                Linux
Installed from:    Gentoo Packages

Sometimes the dialogs in KDE hang. Here is one I can currently reproduce:
1. fire up kwrite
2. write something
3. close
-> The application hangs for a couple of seconds till the dialog shows up.

Have a look at my strace output from:
strace kwrite 2> kwrite_log

The hanging starts exactly at:
gettimeofday({1243469810, 680552}, NULL) = 0
poll([{fd=8, events=POLLIN}], 1, 25000) = 1 ([{fd=8, revents=POLLIN}])
read(8, "l\2\1\1\v\0\0\0\1\0\0\0=\0\0\0\6\1s\0\6\0\0\0:1.895\0\0\5"..., 2048) = 262
read(8, 0x6d4c10, 2048)

in line 1844 of the file.

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Sometimes I get in dialogs of applications an empty dialog box with no text nor buttons (have a look at the screenshot). It takes a couple of seconds till the text shows up. I belief this is the same bug. Unfortunately this one is hard to reproduce so I don't have an strace output.

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Other infos that might be helpful:

$ gcc --version
gcc (Gentoo 4.3.3-r2 p1.1, pie-10.1.5) 4.3.3
Copyright (C) 2008 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ uname -a
Linux gentoo64 2.6.27-gentoo-r5 #1 SMP Mon Dec 15 12:10:28 CET 2008 x86_64 AMD Athlon(tm) 64 Processor 3500+ AuthenticAMD GNU/Linux

Qt version 4.5.1 in /usr/lib64/qt4