Was caused by recent change in image_buffer_rect_update which was writing data to ibuf-rect_float. Apparently, this buffer could point to different render layer than came from RenderResult. Made quick fix for this, which ends up in skipping float buffer update in image_buffer_rect_update and skipping GLSL when image has both byte and float buffers. This will bring speed down a bit, but slower blender is better than broken blender. Proper fix will arrive later this week.