Only the package
virtualbox-guest-X11
is the reason for not working Plasma 5.
With Deinstallation of 
virtualbox-guest-X11
the Plasma 5 will work well, but without changing the size of Guest-window.

The Shared Folder will work fine with installation of
virtualbox-guest-dkms
virtualbox-gues-utils

siductionbox:~$ dpkg -l virtualbox*
Gewünscht=Unbekannt/Installieren/R=Entfernen/P=Vollständig Löschen/Halten
| Status=Nicht/Installiert/Config/U=Entpackt/halb konFiguriert/
         Halb installiert/Trigger erWartet/Trigger anhängig
|/ Fehler?=(kein)/R=Neuinstallation notwendig (Status, Fehler: GROSS=schlecht)
||/ Name                  Version         Architektur     Beschreibung
+++-=====================-===============-===============-================================================
ii  virtualbox-guest-dkms 4.3.28-dfsg-1   all             x86 virtualization solution - guest addition mod
un  virtualbox-guest-modu <keine>         <keine>         (keine Beschreibung vorhanden)
un  virtualbox-guest-sour <keine>         <keine>         (keine Beschreibung vorhanden)
ii  virtualbox-guest-util 4.3.28-dfsg-1+b i386            x86 virtualization solution - non-X11 guest util
un  virtualbox-guest-x11  <keine>         <keine>         (keine Beschreibung vorhanden)

Why can Plasma 5 and virtualbox-guest-X11 not work together?

The Distribution "Netrunner 16" has inside an package
virtualbox-guest-X11
that can work with Plasma 5.
But it also can not change the size of Guest-window.

Hello,

I'm maintaining the siduction's kde packages and also sending patches to kubuntu's packaging, I can assure that plasma 5 works well with virtualbox both on siduction and kubuntu (and I'm not the only one who tested that)

This bug report is not valid; if there's any issue is in virtualbox itself or the virtualbox packaging, also note that in this message on the siduction forum the reporter says that he doesn't have the virtualbox kernel module loaded:
http://forum.siduction.org/index.php?topic=5671.msg46264#msg46264

Closing as invalid, since this is material for a forum user support and not a bug tracker.

Created attachment 93600 [details]
attachment-19949-0.html

Hello,
sorry, my Plasma 5 don't work only when I have installed in the
Guest-system:
virtualbox-guest-X11

With
virtualbox-guest-dkms
virtualbox-guest-utils
the Shared File support is working well and no message achieved.

with regards
Ch. Hanisch


Am 15.07.2015 um 13:20 schrieb José Manuel Santamaría Lema :
> https://bugs.kde.org/show_bug.cgi?id=350234
>
> José Manuel Santamaría Lema <panfaust@gmail.com> changed:
>
>            What    |Removed                     |Added
> ----------------------------------------------------------------------------
>              Status|UNCONFIRMED                 |RESOLVED
>          Resolution|---                         |INVALID
>                  CC|                            |panfaust@gmail.com
>
> --- Comment #3 from José Manuel Santamaría Lema <panfaust@gmail.com> ---
> Hello,
>
> I'm maintaining the siduction's kde packages and also sending patches to
> kubuntu's packaging, I can assure that plasma 5 works well with virtualbox both
> on siduction and kubuntu (and I'm not the only one who tested that)
>
> This bug report is not valid; if there's any issue is in virtualbox itself or
> the virtualbox packaging, also note that in this message on the siduction forum
> the reporter says that he doesn't have the virtualbox kernel module loaded:
> http://forum.siduction.org/index.php?topic=5671.msg46264#msg46264
>
> Closing as invalid, since this is material for a forum user support and not a
> bug tracker.
>

Solution:

In both aptosid-December-2013  host and Ubuntu 12.04 host install VirtualBox 5.0 from Oracle homepage, then the corresponding Guest Additions in the guest systems siduction and Kubuntu 15.04 installed.

Then the essential element:
VirtualBox -> Change -> Display -> acceleration -> not checked in "3D acceleration Enable"

In order to work plasma 5 with all the features of the Guest Additions.

Please give me an answer why this strange action solve the problem.

Greeting
Ch. Hanisch