My system is Lubuntu 15.04 x64 with the PPA for LXQt, updated up to the last package:

    Linux PC-baltasarq 3.19.0-16-generic #16-Ubuntu SMP Thu Apr 30 16:09:58 UTC 2015 x86_64 x86_64 

 When using VLC or SMPlayer, both apps crash as soon as a I press Ctrl+O or select File >> Open or whatever. The crash is not very informative. by itself, so I opened a GDB session for SMPlayer.

$ gdb smplayer 
    GNU gdb (Ubuntu 7.9-1ubuntu1) 7.9
    (gdb) r
    Starting program: /usr/bin/smplayer 
    [Thread debugging using libthread_db enabled]
    Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
    This is SMPlayer v. 14.9.0 running on Linux

    Program received signal SIGSEGV, Segmentation fault.
    0x00007fffee02a0ff in KFileDialog::KFileDialog(KUrl const&, QString const&, QWidget*, QWidget*) () from /usr/lib/libkio.so.5
    (gdb) bt
    #0  0x00007fffee02a0ff in KFileDialog::KFileDialog(KUrl const&, QString const&, QWidget*, QWidget*) () from /usr/lib/libkio.so.5
    #1  0x00007fffee02e37c in ?? () from /usr/lib/libkio.so.5
    #2  0x00007ffff6bedb66 in QFileDialog::getOpenFileName(QWidget*, QString const&, QString const&, QString const&, QString*, QFlags<QFileDialog::Option>) () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
    #3  0x0000000000520fae in ?? ()
    #4  0x0000000000553c71 in ?? ()
    #5  0x0000000000566a07 in ?? ()
    #6  0x00007ffff5e9519c in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
    #7  0x00007ffff66fcfd2 in QAction::triggered(bool) ()
    ...

 $ ldd /usr/bin/smplayer
    linux-vdso.so.1 =>  (0x00007ffee5eaf000)
    libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f69d7619000)
    libQtDBus.so.4 => /usr/lib/x86_64-linux-gnu/libQtDBus.so.4 (0x00007f69d739c000)
    libQtScript.so.4 => /usr/lib/x86_64-linux-gnu/libQtScript.so.4 (0x00007f69d6ed6000)
    libQtXml.so.4 => /usr/lib/x86_64-linux-gnu/libQtXml.so.4 (0x00007f69d6c8f000)
    libQtGui.so.4 => /usr/lib/x86_64-linux-gnu/libQtGui.so.4 (0x00007f69d5f95000)
    libQtNetwork.so.4 => /usr/lib/x86_64-linux-gnu/libQtNetwork.so.4 (0x00007f69d5c43000)
    libQtCore.so.4 => /usr/lib/x86_64-linux-gnu/libQtCore.so.4 (0x00007f69d5752000)
   ...

My environment seems to be correctly set:

    $ printenv | grep QT
    LXQT_SESSION_CONFIG=session
    QT_IM_MODULE=ibus
    QT_QPA_PLATFORMTHEME=lxqt
    QT_PLATFORM_PLUGIN=lxqt
    QT4_IM_MODULE=xim

I've filled an issue in LXQt, but finally the answer I got was the following one:
It seems that the problem is caused by KDE plugin.
"We no longer provide Qt 4 platform plugin, so the plugin loaded is actually from KDE.
In the gdb log, you can see KFileDialog, which is the KDE implementation of Qt file dialog.
This is not related to LXQt. Please report to Ubuntu and KDE developers.
Thanks."

It does not matter whether I'm using the original LXDE session of the distribution, or the LXQt one.

The issue in LXQt:
https://github.com/lxde/lxqt/issues/634

A hint found by a LXQt maintainer: "One thing is pretty weird, though: both SMPlayer and VLC are using the GTK file chooser, not the one from Qt. Other Qt programs like Otter Browser (ppa:otter-browser/daily) or LXImage-Qt do use the regular Qt file chooser.
This is something that shouldn't happen and could be related to your findings."

This is the third time I fill this bug (the very first time in the VLC bug tracker). Hope this time this is the appropriate place.

-- Baltasar



Reproducible: Always

Steps to Reproduce:
1. Install Lubuntu 14.10
2. Upgrade up to Lubuntu 15.04
3. Launch SMPlayer, or B1, or VLC, and try opening a file.

Actual Results:  
The application crashes with a backtrace similar to the one I added above.

Expected Results:  
I should be able to pick up a file to open!