Comment 59 for bug 1535732

No, the backspace bug is not related to this because texts which the user has to enter must be rendered "on the fly" whereas other strings get pre-rendered. It is waste of time when each known string has to be typed character by character on the screeen. This where pre-rendering comes in: All known texts get rendered into an image and then painted on the screen (as i understand). To create such an image offscreen rendering is used. Offscreen rendering paints pixels into an image in memory which is then be used for displaying on the screeen.

And across the offscreen rendering process something goes wrong with some graphic drivers. Maybe the pixel buffer (what offscreen rendering uses) get filled with wrong pixels while the same buffer is read at the same time. See: https://www.opengl.org/wiki/GLSL_:_common_mistakes#Sampling_and_Rendering_to_the_Same_Texture

Just assuming this....