@soliwilos
I've got a new build ready with Qt 5.2.1 -qt-libpng. Could you try this out? box download (to be removed once we have this released or up on the installer preview page).
I've verified that this works on Ubuntu 14.04 and does not have the libpng dependency anymore. Ironically, Ubuntu 14 does have libpng1.2 installed.
The biggest known Linux regression in v1.2.0 is that we don't handle AppIndicators on Ubuntu 13+ properly with Qt 5, but your tray icon should be fine if you're on Gentoo.
A list of changes between 1.1.3 and 1.2 can be found in this post. For Linux, we never released 1.1 through 1.1.3 publicly, so admittedly the rest of those changelogs may take some work to track down.