Hi As of tonight, Scribus 1.5.0+ will only be supported with Qt5. We have had to find some workarounds for some issues, and these will be fixed over time, however Qt5 will bring a number of features and improvements on the back end we require. Primarily, the new Qt Quick controls should offer us the ability to rewrite the Properties Palette with Qt's new XML based GUI design functionality. There's a lot more however that's a big one to note.
For anyone developing or building from source, ensure you update your Qt installation to 5.x. thanks Craig
