Jürgen, didn't you do something with paper settings recently? I notice this when compiling 1.4:
QGraphics.C: In member function `virtual void lyx::frontend::QGraphics::update_contents()': QGraphics.C:173: warning: enumeration value `PAPER_CUSTOM' not handled in switch QGraphics.C:173: warning: enumeration value `PAPER_B3' not handled in switch QGraphics.C:173: warning: enumeration value `PAPER_B4' not handled in switch -- Angus