avalanche of messages from Launchpad on standard error

When I use Launchpad as a desktop application starting it in a console:

{ /usr/bin/webapp-container --app-id=Launchpadlaunchpadnet --webapp=TGF1bmNocGFk --enable-back-forward; }

the application prints lots of messages to the standard error. The window does not handle mouse clicks while this happens, accumulating them into a buffer instead. In particular, scrolling and navigation works only after it has stopped printing.

The messages from a short session attached.

Stack trace:

#0 qt_message_print (msgType=msgType@entry=QtDebugMsg, context=...,
    message=...) at global/qlogging.cpp:929
#1 0x00007ffff77b8fbd in qt_message(QtMsgType, const QMessageLogContext &, const char *, typedef __va_list_tag __va_list_tag *, QString &) (
    msgType=msgType@entry=QtDebugMsg, context=...,
    msg=msg@entry=0x7ffff6095053 "%s", ap=ap@entry=0x7fffffffc938, buf=...)
    at global/qlogging.cpp:245
#2 0x00007ffff77b90f2 in QMessageLogger::debug (
    this=this@entry=0x7fffffffcab0, msg=msg@entry=0x7ffff6095053 "%s")
    at global/qlogging.cpp:261
#3 0x00007ffff5ff9131 in writeToConsole (logType=Log,
    printStack=<optimized out>, ctx=<optimized out>, ctx=<optimized out>)
    at qml/v8/qqmlbuiltinfunctions.cpp:1394
#4 0x00007ffff5ec2202 in QV4::BuiltinFunction::call (that=0x7fffe8033650,
    callData=<optimized out>) at jsruntime/qv4functionobject.cpp:622
#5 0x00007ffff5e8e6ca in call (callData=0x7fffc2d66c28, this=<optimized out>)
    at jsruntime/qv4functionobject_p.h:133
#6 QV4::__qmljs_call_property (context=0x7fffc00193e0, name=..., callData=...)
    at jsruntime/qv4runtime.cpp:915
#7 0x00007fffe00d8f3a in ?? ()

(probably JIT-compiled, confuses gdb).

The offending message gets dumped from <URL: file:///usr/lib/x86_64-linux-gnu/qt5/qml/Ubuntu/UnityWebApps/UnityWebApps.js#line=111 >. This ultimately evaluates to a serial call to console.log, which blocks the application if the output device is slow.

See also <URL: news:1bp21kqu4hqss$.31ga4jgjsbk6.dlg@40tude.net >. I am also told one could use non-blocking I/O for console output.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: webapp-container 0.23+14.04.20140428-0ubuntu1
ProcVersionSignature: Ubuntu 3.13.0-36.63-generic 3.13.11.6
Uname: Linux 3.13.0-36-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.5
Architecture: amd64
CurrentDesktop: Unity
Date: Sat Oct 4 22:25:21 2014
InstallationDate: Installed on 2014-08-20 (45 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417)
SourcePackage: webbrowser-app
UpgradeStatus: No upgrade log present (probably fresh install)