It seems that there are two independent issues:

1) Qt Scene Graph (qsgbatchrenderer) causes access violation if a shader is not found.

2) Qt Quick Text uses curve renderer (at least, shaders associated with curve rendering) in certain situations (in our case, underlined text on Windows), even if it is not explicitly enabled with `renderType`. However, `scenegraph_curve_shaders` is never initialized by Qt unlike `scenegraph_shaders` (see `initResources()` of `qsgdefaultcontext.cpp`).