Cannot mix incompatible Qt library

i'm also now getting this problem on a 13.04 system since todays updates which included some qt libraries...

Cannot mix incompatible Qt library (version 0x40804) with this library (version 0x40803)
Aborted (core dumped)

Status changed to 'Confirmed' because the bug affects multiple users.

I'm affected by this as well. When I try to start any of okular, VirtualBox (the qt GUI), kmail, or AFAICT anything that uses qt4, I get

$ kmail
Cannot mix incompatible Qt library (version 0x40804) with this library (version 0x40801)
zsh: abort (core dumped) kmail

$ okular
Cannot mix incompatible Qt library (version 0x40804) with this library (version 0x40801)
KCrash: Application 'okular' crashing...
KCrash: Attempting to start /usr/lib/kde4/libexec/drkonqi from kdeinit
sock_file=/home/jun/.kde/socket-jun-MacBookAir/kdeinit4__0
Warning: connect() failed: : No such file or directory
KCrash: Attempting to start /usr/lib/kde4/libexec/drkonqi directly
Cannot mix incompatible Qt library (version 0x40804) with this library (version 0x40801)

$ anki
Cannot mix incompatible Qt library (version 0x40804) with this library (version 0x40801)
zsh: abort (core dumped) anki

I've tried recompiling okular from the source package, but I got the same exact error. This has rendered many packages completely unusable for me. I think this bug deserves a high importance rating, unless it's rare (i.e. affecting few people), because AFAICT for those who are affected this bug is seriously crippling.

I appear to have this (or similar) with openscad on Ubuntu 14.04.1 LTS

>> openscad
Cannot mix incompatible Qt library (version 0x40806) with this library (version 0x40804)
Abort (core dumped)

Hi
Could you possibly pastebin the output of apt-cache policy libqt4-opengl

I have the same problem like SA.
This is the output of apt-cache policy libqt4-opengl:
libqt4-opengl:
  Installé : 4:4.8.5+git192-g085f851+dfsg-2ubuntu4
  Candidat : 4:4.8.5+git192-g085f851+dfsg-2ubuntu4
 Table de version :
 *** 4:4.8.5+git192-g085f851+dfsg-2ubuntu4 0
        500 http://ch.archive.ubuntu.com/ubuntu/ trusty/main i386 Packages
        100 /var/lib/dpkg/status
I'm using Ubuntu 14.04 LTS i686 and actually I have only problem with OpenScad.

apt-cache policy libqt4-opengl
libqt4-opengl:
  Installed: 4:4.8.5+git192-g085f851+dfsg-2ubuntu4.1
  Candidate: 4:4.8.5+git192-g085f851+dfsg-2ubuntu4.1
  Version table:
 *** 4:4.8.5+git192-g085f851+dfsg-2ubuntu4.1 0
        500 http://gb.archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu/ trusty-security/main amd64 Packages
        100 /var/lib/dpkg/status
     4:4.8.5+git192-g085f851+dfsg-2ubuntu4 0
        500 http://gb.archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages

FWIW installing the tarball compiled openscad from the openscad home was painless and works fine...

Scratch that last comment the tarball runs fine at first and then crashes with the same incompatible QT error as before.

However building openscad from source (openscad-2015.03-1) results in a working version - building takes ~20minutes and by way of compensation the new version is nicer.