What seems to be happening here is a sort of crosstalk or feedback. His brain is still recognizing the glyphs, but those neurons are sending unwanted signals elsewhere in his visual cortex which scramble the perceived image.
My interpretation of this case is that the image we perceive consciously is a combination of the raw visual data and various recognition modules, so that we don't just perceive "a curved line crossing back on itself in the lower right of the image" plus "the abstract notion of the number 8", but we see the number 8 localized where the line forming it is. Same with any other symbols, objects, faces etc.
Because of this, the neurons that represent the conscious perception of a certain section of the visual field must receive both "low-level" information (the curves forming the digit, their color, the color of the background), but also "mid-level" recognition output ("the digit 8"). So if the neuron(s) recognizing the 8 act up and send scrambled signals, they can scramble the whole conscious perception of the corresponding area of the visual field. The fact that it also disrupts his conscious perception of faces overlying the digit confirms this.