Unable to debug: WPushButton(...) does not have a property named "layoutAlignment"

I built a skin (http://www.mixxx.org/forums/viewtopic.php?f=8&t=8578) and I'm wondering why the log is filled with lines like this for Sliders, Buttons, VUMeters etc. although I declared alignemt in qss stylesheet.

Example:
Warning [Main]: WVuMeter(0x715d750, name = "SamplerVU") does not have a property named "layoutAlignment"
Warning [Main]: WLabel(0x6de0570, name = "SuperWetDryLabel") does not have a property named "layoutAlignment"
Warning [Main]: WPushButton(0x6d2b210, name = "EffectSelectorButton") does not have a property named "layoutAlignment"
Warning [Main]: WPushButton(0x87ad920, name = "SkinSettingsButton") does not have a property named "layoutAlignment"
Warning [Main]: WStarRating(0x9a868e0, name = "DeckStars") does not have a property named "layoutAlignment"

In qss it looks like this for Buttons, Sliders etc. :
#DeckStars {
    qproperty-layoutAlignment: 'AlignHCenter | AlignVCenter';

I learned the qss settings from default skins like LateNight. What am I doing wrong?