Texture corruption when multiple QQuickWindows are used

When multiple QQuickWindows are used and in at least two windows a new texture is created at the same time, there is a strong visual corruption. So far we only noticed the corruption with Intel graphics and only if the threaded renderer is NOT used - both basic and window renderer show the problem.

Find attached a minimum example which illustrates the issue when run through qmlscene. When clicking anywhere in the main window the texture should be updated in both windows, but this results in visual corruption as can be seen in the attached screenshot.

Output when run with QSG_INFO enabled on my system:

QtQmlViewer(6737)/(default) QSGRenderLoop::instance: QSG: basic render loop
QtQmlViewer(6737)/(default) KIconLoaderPrivate::initIconThemes: "Theme tree: (Oxygen)"
QtQmlViewer(6737)/(default) QSGAtlasTexture::Manager::Manager: QSG: texture atlas dimensions: 512 x 512
QtQmlViewer(6737)/(default) QSGContext::renderContextInitialized: R/G/B/A Buffers: 8 8 8 8
QtQmlViewer(6737)/(default) QSGContext::renderContextInitialized: Depth Buffer: 24
QtQmlViewer(6737)/(default) QSGContext::renderContextInitialized: Stencil Buffer: 8
QtQmlViewer(6737)/(default) QSGContext::renderContextInitialized: Samples: -1
QtQmlViewer(6737)/(default) QSGContext::renderContextInitialized: GL_VENDOR: Intel Open Source Technology Center
QtQmlViewer(6737)/(default) QSGContext::renderContextInitialized: GL_RENDERER: Mesa DRI Intel(R) Ivybridge Desktop
QtQmlViewer(6737)/(default) QSGContext::renderContextInitialized: GL_VERSION: 3.0 Mesa 10.1.2
QtQmlViewer(6737)/(default) QSGContext::renderContextInitialized: GL_EXTENSIONS: GL_EXT_blend_color GL_EXT_rescale_normal GL_EXT_framebuffer_multisample GL_EXT_separate_shader_objects GL_ARB_provoking_vertex GL_ARB_transform_feedback_instanced GL_EXT_texture_object GL_AMD_conservative_depth GL_EXT_texture_env_combine GL_EXT_transform_feedback GL_ARB_timer_query GL_EXT_secondary_color GL_ARB_window_pos GL_EXT_texture_swizzle GL_OES_read_format GL_ATI_texture_env_combine3 GL_ARB_vertex_array_object GL_ARB_texture_env_dot3 GL_EXT_texture_sRGB GL_EXT_texture_cube_map GL_EXT_texture_sRGB_decode GL_ARB_copy_buffer GL_ARB_vertex_type_10f_11f_11f_rev GL_ARB_texture_storage GL_KHR_debug GL_ARB_instanced_arrays GL_ARB_fragment_coord_conventions GL_ARB_color_buffer_float GL_ARB_texture_mirrored_repeat GL_SGIS_texture_lod GL_EXT_subtexture GL_ARB_texture_swizzle GL_ARB_texture_compression GL_EXT_gpu_program_parameters GL_EXT_provoking_vertex GL_ARB_point_parameters GL_ATI_draw_buffers GL_NV_depth_clamp GL_AMD_shader_trinary_minmax GL_ARB_ES2_compatibility GL_ARB_draw_buffers_blend GL_AMD_seamless_cubemap_per_texture GL_ARB_fragment_program_shadow GL_ARB_debug_output GL_NV_texture_rectangle GL_ARB_draw_elements_base_vertex GL_EXT_texture_shared_exponent GL_SGIS_generate_mipmap GL_ARB_shading_language_420pack GL_ARB_vertex_buffer_object GL_EXT_texture_env_dot3 GL_AMD_draw_buffers_blend GL_EXT_texture GL_ARB_transform_feedback2 GL_ARB_shader_texture_lod GL_ARB_transform_feedback3 GL_ARB_shading_language_100 GL_ARB_occlusion_query2 GL_ARB_shader_bit_encoding GL_ARB_texture_query_levels GL_AMD_performance_monitor GL_SGIS_texture_border_clamp GL_EXT_texture_lod_bias GL_ARB_half_float_pixel GL_ARB_robustness GL_EXT_texture_filter_anisotropic GL_IBM_texture_mirrored_repeat GL_EXT_separate_specular_color GL_EXT_texture_compression_s3tc GL_EXT_texture_array GL_EXT_point_parameters GL_ARB_framebuffer_sRGB GL_EXT_draw_range_elements GL_EXT_blend_func_separate GL_ARB_vertex_program GL_EXT_texture_compression_dxt1 GL_EXT_timer_query GL_EXT_draw_instanced GL_ARB_point_sprite GL_ARB_texture_multisample GL_ATI_texture_float GL_EXT_fog_coord GL_ATI_separate_stencil GL_EXT_framebuffer_blit GL_ARB_sample_shading GL_ARB_texture_mirror_clamp_to_edge GL_S3_s3tc GL_ARB_multisample GL_INGR_blend_func_separate GL_EXT_shadow_funcs GL_EXT_texture3D GL_EXT_framebuffer_sRGB GL_MESA_pack_invert GL_EXT_packed_float GL_ARB_seamless_cube_map GL_ARB_shader_atomic_counters GL_ARB_ES3_compatibility GL_EXT_shader_integer_mix GL_EXT_compiled_vertex_array GL_ARB_sync GL_EXT_vertex_array GL_ARB_texture_rectangle GL_NV_texgen_reflection GL_ARB_map_buffer_range GL_ARB_pixel_buffer_object GL_ARB_vertex_array_bgra GL_NV_texture_env_combine4 GL_ARB_uniform_buffer_object GL_EXT_blend_minmax GL_EXT_multi_draw_arrays GL_ARB_texture_float GL_EXT_texture_env_add GL_ARB_sampler_objects GL_EXT_bgra GL_ARB_map_buffer_alignment GL_NV_blend_square GL_ARB_depth_buffer_float GL_ANGLE_texture_compression_dxt3 GL_ANGLE_texture_compression_dxt5 GL_EXT_texture_integer GL_ARB_texture_rgb10_a2ui GL_EXT_texture_edge_clamp GL_ARB_fragment_shader GL_ARB_occlusion_query GL_3DFX_texture_compression_FXT1 GL_ARB_explicit_attrib_location GL_EXT_draw_buffers2 GL_EXT_framebuffer_multisample_blit_scaled GL_NV_primitive_restart GL_ARB_internalformat_query GL_ARB_texture_env_add GL_MESA_texture_signed_rgba GL_EXT_texture_rectangle GL_SUN_multi_draw_arrays GL_APPLE_object_purgeable GL_EXT_vertex_array_bgra GL_ARB_clear_buffer_object GL_EXT_blend_subtract GL_ARB_multitexture GL_EXT_framebuffer_object GL_ATI_envmap_bumpmap GL_APPLE_vertex_array_object GL_EXT_abgr GL_MESA_window_pos GL_ARB_draw_buffers GL_SGIS_texture_edge_clamp GL_ARB_texture_env_combine GL_ARB_vertex_shader GL_EXT_blend_equation_separate GL_ARB_shader_objects GL_ARB_texture_compression_rgtc GL_ARB_half_float_vertex GL_ARB_invalidate_subdata GL_NV_light_max_exponent GL_NV_conditional_render GL_EXT_pixel_buffer_object GL_EXT_packed_depth_stencil GL_ARB_blend_func_extended GL_ARB_texture_border_clamp GL_ARB_shadow GL_IBM_multimode_draw_arrays GL_ARB_draw_instanced GL_ARB_fragment_program GL_EXT_copy_texture GL_ARB_texture_env_crossbar GL_EXT_texture_compression_rgtc GL_EXT_texture_snorm GL_ARB_texture_gather GL_ARB_vertex_attrib_binding GL_ARB_get_program_binary GL_EXT_polygon_offset GL_EXT_stencil_two_side GL_ARB_depth_clamp GL_ARB_texture_storage_multisample GL_ARB_texture_cube_map_array GL_ARB_depth_texture GL_ARB_shading_language_packing GL_ARB_texture_rg GL_IBM_rasterpos_clip GL_OES_EGL_image GL_EXT_packed_pixels GL_EXT_stencil_wrap GL_ARB_framebuffer_object GL_ARB_vertex_type_2_10_10_10_rev GL_ARB_texture_cube_map GL_APPLE_packed_pixels GL_ARB_texture_non_power_of_two GL_ARB_conservative_depth GL_ARB_transpose_matrix GL_NV_packed_depth_stencil GL_ATI_blend_equation_separate GL_ARB_texture_query_lod