There are several issues with LibreOffice icons in Ubuntu 12.04:
- icons are not displayed at all
- icons are duplicated
- white square is displayed instead real icons and it is not responsive
- a grey empty area are displayed instead the icon
- LibreOffice programs are not listed in opened applications and they are not visible even if you use Alt + Tab
So, when you run, for example the Calc, the icon is sometimes the icon is present in the launcher, but there is an empty space on the launcher just above the Calc icon or icon is invisible. This bug is a cosmetical one however in a LTS distribution this does not look professional
Users that use KDE can experience the issue icons not showing in the Office menu.
The only solution we found in GNOME is to lock the icons to the launcher. After that number of the issue will be lower, but they could still appear.
If you cannot see running LibreOffice application even with Alt + Tab, you can use a workaround - Super key + W will show all open windows. Super key is usually the Windows button.
Currently, problem in KDE environment can be solved by using the LibreOffice ppa-repository:
# sudo add-apt-repository ppa:libreoffice/ppa
# sudo apt-get update
# sudo apt-get upgrade