The attached screenshot shows a strange graphical glitch (straight lines) with the newest version (8.51) of the HD texture pack. I have tried both the 2160p and the 1080p version with no difference in the outcome. The lines disappear when I disable custom textures.
Edit: On another person's PC, which still had an old version of the texture pack (8.1) installed, the lines were not present. After an update to 8.51, however, they appeared there as well.
Edit: On another person's PC, which still had an old version of the texture pack (8.1) installed, the lines were not present. After an update to 8.51, however, they appeared there as well.