Both sides of the spyglass texture have the glass part, where you're supposed to be looking through. In the 1.17 snapshots, you would hold the spyglass upside down with the front facing downwards, and the top would not show the glass. Now, each side has the glass part while only the front is supposed to, but the spyglass is still held upside down.

Only one side is supposed to have the glass part, and that is the front, which you normally don't see in first person.