Comment 3 for bug 1015292

The error from Qt get's generated once xcb detects the error at the connector, which Qt doesn't handle by default:

(gdb) p xcb_xfixes_id
$37 = {name = 0xb2433b28 "XFIXES", global_id = 2}
(gdb) n
Breakpoint 3, xcb_get_extension_data (c=0x1fc9b0, ext=0xb243c02c) at ../../src/xcb_ext.c:85
85 ../../src/xcb_ext.c: No such file or directory.
(gdb) n
87 in ../../src/xcb_ext.c
(gdb) p c->has_error
$39 = 1

....

Qt:

void QXcbConnection::initializeXFixes()
{
    xcb_generic_error_t *error = 0;
    const xcb_query_extension_reply_t *reply = xcb_get_extension_data(m_connection, &xcb_xfixes_id);
    xfixes_first_event = reply->first_event;
...

As this is causing the X11 server to blow as well, I believe this is probably related with an issue on the xrandr side, as it's the first extension Qt loads before moving on with the application.